Where did you get Windows 7? If you burned the DVD yourself, try burning another using ImgBurn at 4x speed.
WHile you still have XP, make sure you have latest BIOS version update. If so, reset your CMOS: http://pcsupport.about.com/od/fixthe.../clearcmos.htm
Try wiping the HD before install: SSD / HDD : Optimize for Windows Reinstallation
Boot the Windows 7 DVD to Custom install, use Drive Options to partition and format before install. Clean Install with a Upgrade Windows 7 Version
If problems persist, test your HD using maker's diag/repair full CD scan: Hard Drive Diagnostics Tools and Utilities (Storage) - TACKtech Corp.
Then boot the DVD, press Shift + F10 to open a Command Line and run Disk Check
Test your RAM using memtest86 for 5-6 passes. Swap RAM sticks, remove all but 2gb to try install.
Here are also some tips on getting a perfect install, based on hundreds done here: http://www.sevenforums.com/installation-setup/125874-re-install-windows-7-a.html#post1086729