Precision T3400

There are Zero upgrades from XP To windows 7.  This will require a scorched earth Total Reinstall.

You may have many problems going to 64 bit OS.  If you cannot find Drivers for your devices check to see if there are windows VISTA Drivers for your Video and Audio etc.

Run the Windows 7 Upgrade Advisor ... it can identify some potential problems you could face.

www.microsoft.com/.../details.aspx

All of what I said is true, but note what SpeedStep has said ... there is not upgrade path from XP to 7, and no upgrade path from a 32-bit OS to a 64-bit OS - it will require a fresh install of 7x64.

EDIT:
woah ... sorry SpeedStep ... my post read "what I said is true, but not what SpeedStep has said" ... meant to read "what I said is true, but NOTE what SpeedStep has said" :)

And because Windows 7x64 is supported by Dell on this machine, you should have no hardware difficulties.  Software you have loaded on it could be a different story.

http://support.dell.com/support/downloads/driverslist.aspx?os=W764&catid=-1&dateid=-1&impid=-1&osl=EN&typeid=-1&formatid=-1&servicetag=&SystemID=PRE_T3400&hidos=WLH&hidlang=en&TabIndex=&scanSupported=True&scanConsent=False

The Bad part is that they require you to do a clean install which loses all your apps etc.

For anyone trying this I always recommend getting a new hard drive and keeping the old drive with XP as a backup.