Dimension 8300 Video Card Upgrade Info Needed

I have a Dimension 8300  (Purchased in 2004) with 4Gb of RAM and a NVidia GeForce FX5200 Video card in the AGP slot.  I installed Win& 32-bit about two weeks ago.  Everything is working fine BUT this computer is now my wife's and shee likes to play Spider/Regular solitare, Jewel Quest and several other simple games.  I bought her a nice flatpanel to go with the upgraded computer.  The problem is that the games are very, very slow.  The speed score for the video portion of my system is 1 and the minimum that the Games need is a 2.  I purchased a Visiontek HD3650 agp card with 512Mb on board form NewEgg.  No matter what I do I can't get it to install on my system.  Visiontek website is no help!!!!  Newegg was very nice and agreed to to take the card back based on incompatilbility.  I found the list of systems heirarchy of video cards published by Dell (I think).  It only lists to cards, a AGP Radeon HD4650 and a NVidia FX5950PRO AGP as known cards that will operate with my system.  Due to the fact that these are hard to find (Think expensive or rebuilt), I am looking for other possibilities in video cards.  I see many AGP cards for sale but trying to get them to work with my system and be WIN7 compatible is an unknown.  Please help me.  Can anyone give me a suggestion for a better video card that currently works on their Dim 8300 with WIN7 & 4Gb of RAM and a Pentium 4?  What problems did you have with the installation.  PS:  I do not know which power supply I have with my system.  The specification in the book say I have either a 250Watt or a 330Watt.  Will the power supply be an issue?