I used to own around 3. They are very difficult to upgrade (anything more than just a GPU / stick of RAM). Without modding case (think dremel) - the easiest way is to buy a new case ...
Then the Power Supply fittings would not transfer for me (Due to power input from wall socket on the wrong side *read *- i needed a new PSU). Again, i seriously considered the dremel ... but for $40 it was over.
Good Luck !!
On the bright side - Dell power supplies are actually UNDER rated. They are VERY STURDY !! Yeah Dell !