I have a Dell C521 and my friend (who does not do any gaming) agreed to trade with me for his Dell E521. The E521 is a standard size tower. Will this eliminate the problems I was having trying to upgrade the C521 because of the sheer size?

well i dont whether the smaller case would have stopped you upgrading however bigger cases are better (airflow, easir to work on, more room for stuf...) just as long as it has a pci express slot X16 or X8 as the same size as 16; (or an AGP slot) there is no reason for it not to work.

I imagine the powersupply is the real limiting factor on how much graphics power you can cram in.

Open the case, look at the label of the power supply. Tell us what is written there. We are concerned mainly about how many amps you have on the 12v rails. The combined figure is very important also.

You would be able to use full size single slot video card's, but no dual slot cards because of the BTX type layout of the box.
And the psu is upgradeable with almost any standard ATX unit.

Have you done this yourself? I was reading a review which told me that I would have to make modifications to fans shrouds, etc.

AC INPUT(50-60Hz): 100-120V~/9A
200-240V~/4.5A
DC OUTPUT: +5V =/22A, +3.3V =/17A
+12VA=18A, +12VB=//18A
-12V=/1A, +5Vfp=2A
+5V AND +3.3V SHALL NOT EXCEED 150W
+12VA AND +12VB SHALL NOT EXCEED 264W
MAX OUTPUT POWER: 305W

Depending on the video card, you are going to need to upgrade your power supply also. It has only 22 amps on the 12v rails.

well then it depend what GPU you really want. GTX280? or 7100LE? both have very different requirements

No I haven't.
Here's a thread from the DCF, includes photos
http://www.dellcommunity.com/suppo [...] .id=159213

I would rather not make modifications. What is the best card I can just plug and play? Given the mobo design and power supply capability.