Once you've got XP running, be sure to install the latest security patches from Microsoft.  There is an online tool to help with this at: http://update.microsoft.com/ (Internet Explorer required for this tool). For first-time users this process will take about 20 minutes with a high-speed internet connection, and will usually require several restarts. Several patches need to be installed singly, as well as one or two groups of related updates.

Then, you're going to need software.  The VersionTracker Windows editorial team has compiled three lists of downloads for the Mac user who occasionally boots into Windows:

• Essentials: if you have to use XP for any length of time, you're going to need a browser, etc.
• Games: lets face it, there are a few titles we'd all like to play that haven't been ported to OS X yet.
• Specialty Device Drivers/Utilities: nominated by the MacFixIt readership, these are the tools you need to interface with devices that up until now, have never been able to talk to a Mac

This is just the starting point.  There's always more coming in, at http://www.versiontracker.com/windows/

Essentials

• AVG Free
  Well-known anti-virus protection tool. AVG Free is available free-of-charge to home users for the life of the product.
• Spybot Search & Destroy
  Searches your hard drive for so-called spy- or adbots; little modules that are responsible for the ads many programs display.
• Ad-Aware
  Multi-component detection and removal utility that scans memory, registry, hard, removable and optical drives for known datamining, aggressive advertising, and tracking components.
• Firefox
  Stable and relatively secure Web browser for Windows XP.
• Google Desktop
  desktop search application that provides full text search over your email, computer files, chats, and the web pages you've viewed. The next best thing to Spotlight under Windows.
• IrfanView
  Fast image viewer and converter that supports animated GIFs and many other image formats.
• Error Nuker
  Scan the Windows Registry to identify errors and ways to optimize the performance of the Windows Registry.
• EvidenceNuker
  Removes data from cache, history, cookies, temp files and other folders that contain evidence of internet activities.
• PodUtil
  A management program for the Apple iPod. PodUtil can copy the music from your iPod back to your computer.
• iPod Music Liberator
  Allows you to copy music from your iPod to any computer, filling in a missing feature of iTunes.
• Trillian
  Chat client with support for AIM, ICQ, MSN, Yahoo! Messenger and IRC - login with multiple AIM/ICQ/MSN/Y! accounts at the same time.
• FolderSync
  File compare, diff and synchronization utility.
• 7-Zip
  ZIP-compatible file archiver with highest compression ratio. The program is fully integrated to Windows Shell, so all archive operations like extracting, compressing and browsing can be executed using usual Windows Explorer.
• Folder Lock
  Fast file-security software that can lock, hide or encrypt any number of files, folders, pictures and documents in seconds.
• SnagIt
  All the screen capture and editing functionality youíll ever need.
• VersionTracker Pro
  Find, download and install software and driver updates.
• Windows Media Player
  Thought you'd never be able to synchronize that Windows Media portable music player with your Mac? Thanks to dual-boot you can with the aid of the popular Media Player software.
• Microsoft DirectX
  An advanced suite of multimedia application programming interfaces (APIs) built into Microsoft Windows, required by some of the below games.

Games

• Half-Life 2
  Gordon Freeman is back! Along with scientist Eli Vance and his daughter Alyx, your mission is to save the world from total alien domination.
• F.E.A.R
  A paramilitary force infiltrates a multi billion dollar aerospace compound taking hostages, but issuing no demands. The government responds by sending in its best special operations teams, only to have them obliterated. Live footage of the massacre is cut short by an unexpected wave of destruction that leaves military leaders stunned and in disbelief.
• The Elder Scrolls IV: Oblivion
  Oblivion is a single-player game that takes place in Tamriel's capital province, Cyrodiil. You are given the task of finding the hidden heir to a throne that sits empty, the previous emperor having been killed by an unknown assassin. With no true Emperor, the gates to Oblivion (the equivalent of hell in the world of Tamriel) open, and demons begin to invade Cyrodiil and attack its people and towns.
• Battlefield 2
  Players will choose to fight for one of three military superpowers: the United States, the Chinese, or the newly formed Middle East Coalition. Armed with the latest modern weaponry, players can take control of any of the game's 30 vehicles to engage in major conflicts with over 64 players in some of the largest online battles on the PC.

Device Drivers/Utilities

• Mobile Master
  Let's you synchornize and manage various phones and other handhelds that currently will not play with Mac OS X. You can synchronize mobile phones (addresses and calendar) with Outlook (97-03), Outlook Express, Windows adress book, Lotus Notes, Netscape/Mozilla/Thunderbird, ACT!, Palm Desktop, Eudora, The Bat, Opera.
• Microsoft ActiveSync 4.1
  Synchronization software for Windows-powered Pocket PCs.
• Garmin USB GPS
  Can manage and manipulate USB-based Garmin GPS devices.