Some i7 CPUs may work - the quad core ones won't.  The increase in the RAM ceiling and support for a quad i7 requires a replacement system board (not just a CPU upgrade).

Yes, the system will take standard 2.5" SSDs in place of spinning hard drives.

so is it possible to upgrade the board as well?

Yes, but it will markedly increase the cost of the upgrade.

thanks for your answers! How would I go about getting a price?

ok thanks  that's not out of line, what about which i7 processor will it run what do you guess that would cost

You can do a search for a quad-core M6600 board -- or try a Dell parts reseller.  My guess is you'll be looking at well over $400-500 for a working board, used.

The unit cost me 2800 two years ago I just built a new one on dell site it was 4800

You can probably get $1,000 or more for the system by selling it, and put the $1000 in upgrades toward a newer system - that's what I'd do in this situation.