It may invalidate your warranty with DELL if you DIY, but I see no reason why it shouldn't work ... ATI normally work well with Intel-based chipsets, but the ATI software supplied with the cards can be unstable and may need a bit of twitching.
I used a ATI Radeon 9800 256Mb on my personal PC but had to upgrade my old Intel-based Celeron-powered motherboard due to overheating issues. The nForce-based motherboard and AMD processor which replaced my gear were somewhat unsuitable with the RADEON which forced me to switch to nVidia's GeForce FX 256Mb AGP 8x.
Bottom line is that it will work, but please check with DELL before making any changes to your PC and always check the shop's return policy before purchasing any product.
