Can you put another MB in there? Sometimes DELL cases are slighly nonstandard and dislike non-DELL motherboards...
I second that.
I had two at work that we bought really nice, new CD-R drives for, and I had to take one home, rip the old 8x out of my wife's computer, and bring it into work because the MOBO wouldn't recognize anything faster than a 12x for some reason, on either of them.
Also, there is RAM to consider.
If you upgrade the MOBO, your old RAM probably won't work.
The vid card should work to get you by, but won't be optimal on a new MOBO.