Dell Power Supply or All In Wonder 9800 Problem ?

[1--Eye--Worm]

I'm having a problem with low frame rates and lines through the screen and choppy game play on Call of Duty. At first I thought it was connection lag, but on different servers I was getting the same thing. So I started to play with the Catalyst settings. When I have the settings on Balanced the performance is very poor. The higher the setting the better it gets, but I notice my frame rates don't change from 90fps max, and then when it lags it drops down to 20fps. So I uninstalled Call of Duty and the display drivers. I updated the graphic drivers to 4.12 catalyst with the control panel and then reinstalled Call of Duty. Now when I play COD online with no Patches it works fine, no lag, but the frame rates are lower at about 60fps max with same settings. So I install the COD patch version 1.5 and then back to the lag. So very p**sed and disgusted I decide to reformat since I haven't done it in some time. I reformated updated Windows with SP2 updated my Bios and my chipset drivers to the latest revision. I then reinstalled my 9800 PRO with the updated drivers ( 4.12) and still same problem 60fps when I was pulling 90fps, and lag at different points of gameplay. So I did a little research at different forums and so on and found out that my Dell's power supply is only 250W and the card reqires at least a 300W. Some people say I've got a bad patch so tried different downloads of the same patch, but same thing. I'm wondering if it may be a combinatin of things like the power supply and heat. My Case is full to the hilt and Dell cases arn't that great with cooling. I've heard of people loosing fps from overheated cases. I'm wondering if I buy a 450W power supply and a different case would that help and would I be able to fit my motherboard and cpu in the other case. I do eventually plan on updating my cpu, but not right now. I really would rather just transfer the board and HD and everything else into another case. i have been on the Dell forums and some say the PSU can be changed. They also say the board will fit but the front power button will either have to be riged or somthing.

Specs :
Dell Dimension 8300
2.6 ghz P4 800mhz front side bus
120gb HD
All In Wonder 9800 PRO 128
Samsung DVD/CD ROM drive
Nec DVD+RW drive
Iomega 100mb external drive
Creative Soundblaster Audigy Gamer
Intergrated Intel PRO/100 VE Network connection
Linksys LNE100TX(v5) Ethernet card