This is pretty long but hopefully comprehensive. I suggest you print it out to use as a future reference. Hopefully it'll fit on one page
 
When you change drivers, you should not just overwrite one set with the other. Whilst that works with other types of drivers and it can work sometimes with v/card drivers, it is best to use Add an Remove Progs from the Control Panel to remove previous drivers first. XP professes to remove driver entries from the registry and with all the many driver exchanges I have carried out I have found nothing to the contrary
 
Sometimes nVidia alters the root files of its drivers and if you overwrite these you will get a conflict and of course problems.
 
To ensure all remnants of your existing drivers have been removed:
Click-START then RUN and type in the dialogue box regedit and then click OK.
 
You will then be faced with a drop-down list. Click the cross in the box next to HKEY_CURRENT_USER. When it opens, click on the cross next to SOFTWARE. Scroll down and remove any reference to NVIDIA CORPORATION by right clicking on it and deleting it.
 
Once you've done that, close all the boxes up and repeat the same procedure with the HKEY_LOCAL_MACHINE. You can then return to your desktop. I have not had to do this with XP, but follow this routine:
 
1. Go into Add and Remove Programs and click on Remove NVIDIA Windows 2000/XP Display Drivers.
 
2. Then click Yes to remove them from the registry.
 
3. If it asks you to remove nView profiles, obviously click Yes if you haven't set any, or No if you have. Personally I haven't found the need for them.
 
4. Then click Yes to restart.
 
5. After rebooting, a Wizard will ask if you want to Install software (your drivers) automatically or from a specific location.  
 
6. Click on Specific location and then on Next.<br>
 
7. You will then get another box in which you should click where it says Don't search, I will choose the driver to install, Then on Next.
 
8. In the next box, click on Display adapters and then Next.
 
9. This box has a list of graphics/video cards but ignore them. Click on Have Disk and then on Next.
 
10. This will bring up a box called Install From Disk.
 
11. Click on the Browse button and when the Locate File box pops up, direct it to where you have the driver located, that you wish to install.
 
12. Then click on the driver to expose the display file, usually a nv4_disp or a nv4_disp.inf file. At the same time the file will appear in the File name box below.
 
13. Click on Open.
 
14. This will return you to the Install From Disk box, where the filepath will be displayed opposite the Browse button.
 
15. Click OK.
 
16. The next box will will show your card type, e.g. NVIDIA Geforce 3 Ti 500. Just click Next and it will start to install the drivers.
 
17. Within a split second, a warning box will appear. Completely ignore this as it is pure bull from Microsoft. nVidia are the experts at making drivers, not MS. Click on Continue Anyway and the drivers will install.
 
18. Finally click on Finish when it arrives.
 
A pop-up balloon will appear near your clock in the bottom right corner, confirming the installation is complete.
 
You are then ready to adjust your card and refresh rates and off you go. Eezy peezy, lemon squeezy. Have fun.  
Good luck and if you have any further problems pop back and someone will sort you out.