The tech at CompUSA needs some remedial training -- I had a Gigabyte H67 microATX with Core i3 CPU installed in a Dimension 3000 chassis. (The B110/1100/2400/3000/4600/4700 all share the same chassis and front panel wiring.) And, to finish it, I modified the front audio connector to fit a standard 2x5 header. To top it off, I had the 2tb hard drive set up for a Windows 7/OSX 10.6 Snow Leopard/Ubuntu triple boot. (Yes, I had what was probably the world's only Dell Dimension 3000 Hackintosh.)
The main concern is that the cables are short and may not reach the headers on some boards. The Gigabyte 1155 board (with UEFI BIOS and solid capacitors) I used didn't have that problem.