Windows 7 Screen Resolution

Hello,
I am using windows 7 ultimate on dual Boot system.One is windows 7 and other is windows XP.
There is one problem regarding screen resolution.Whenever i switch on my PC screen resolution doesnt come full.It is always shorter than the actual screen on my monitor.However on XP it is fine.I have downloaded drivers from DELL support site.
My computer specification are,

Dell Optiplex GX 620
3.8 GH Processor
250 GB Hard Disk
1 GB Ram
Intel Motherboard

Kindly Help me in resolving this issue.

You say "when I switch on my PC screen resolution doesn't come full". When you first power on the video card is defaulted to the basic VGA mode and no dirvers have yet been loaded. If this is the actual problem, it's not the Operating System as it too has not been loaded yet. The problem is in the Video card and it's default VGA mode and if this is the problem then it's a hardware problem in the Video card.

also screen is not comming full on my wide screen LCD monitor . and win7 is not giving the option of 1400x900 resolution, but in xp it is working fine.

Thanks,

I have Nvidia Getforce FX5500 256MB AGP card, There is no driver for this AGP Card for Windows 7 on Nvidia official site, but only for XP and Vista, I installed Vista Driver on Win7 its working but screen resolution is not going for 1440x900(wide) which is recommended setting by my HP w1707 LCD Monitor. (win7 is giving only 1280x960 which is not wide and leaving some space both left and right side)

Try using Powerstrip if all else fails; you can actually add new custom resolutions using that software. Although i think it's shareware now with a 30 day trial period... EnTech Taiwan | Utilities | PowerStrip I used it to add resolutions that Catalyst would not normally support..