You should be able to right click on your desktop and under settings it well say xxxxxxx monitor on Geforce XXXXX. If it is a GF4Ti series card, you can't improve it much for $125. It may be a GF2ti 64MB DDR, or even a GF2MX400 64MB, or GF2 GTS 64MB, GF4MX, etc. Any of those those DX 7 cards would be definately worth replacing within your budget, as would GF3 or GF3Ti200 DX8 cards.
Are you in the USA? If so, For $125, best chocie would be a radeon 9600XT or save money on a Radeon 9600 pro for just over $100. For $113, this new <A HREF="http://www.gameve.com/gve/store/productdetails.aspx?sku=VC-9500PRO" target="_new">Radeon 9500 pro</A> would be a nice performer and is faster than the 9600pro and pretty equal to the 9600XT. (shoot, it says backorder now, was in stock last night) The best you can do for around that price is a used/refurbished Radeon 9700 pro.
Now you may be wondering why all these are ATI cards. Simply because they offer the best bang for your price range. You need to spend about $200 before the clear best choice is a NV GF6600GT. The GF FX series doesn't compete with the Radeons for the same price, so avoid them. Another cheap option for you would be to buy a cheap used GF4 Ti4200, 4400, 4600 card. Only DX 8 cards, but still a good bang for the buck.
From best performer to worst, and most expensive to cheaperst, I would say choose from theses cards:
Used Radeon 9700 pro
New Radeon 9600XT or 9500 Pro
New Radeon 9600 Pro
Used GF4 Ti4x00
Edit: Cheap new Radeon 8500le
<A HREF="http://service.futuremark.com/compare?2k3=3400555" target="_new"> My</A>
<A HREF="http://service.futuremark.com/compare?2k1=8268935" target="_new">Gamer</A>
<P ID="edit"><FONT SIZE=-1><EM>Edited by Pauldh on 02/02/05 08:31 AM.</EM></FONT></P>