How many watts is your power supply? I found that with all I had in my system that my graphics card was running a lil slow and had some lag. When I upgraded my power supply from 300w to 550w (a bit much and you could use less) the lag seemed to be gone and the system seemed to run a lil faster.
I upgraded my Dell d4600 a tad over christmas. Now I have a AIW ATi Radeon 9800 pro 128mb and 1gb DDR PC2700 ram, a significant improvment from the old Geforce FX5200 and 512 ram. Anyhow I now run my games at 1024x726 32 bit colour. The problem is I get framerates in the low 20-high 40s running on medium, high, even low running games like UT2k4, BF Vietnam. Now I may have made a mistake with the power supply, I have the card sharing power with the hard drive, but the manual said to do so. Another thing that may be causing the slow down is this 'AGP acceleration' and it's current setting of 'off'. I tried setting it to 4x (2x cannot be selected, board dosen't seem to support it) but some sort of self test wouldn't allow it to be set at 4x so I'm stuck with it set to 'off'. And my final theory is that my processor (P4 2.8ghz, 533 FSB) is bottlenecking the card. Anyhow, any suggestions as to improving performance?