I would invest in a 5.25 slot fan controller. Newegg has a thermaltake for $12.99 plus shipping. Just do a search using their software. Fan controller, fan rpm adjuster, etc. I use a max of 2500 rpm for all my fans; my ps runs at 900, and cpu fan around 1400 using the hardware monitoring bios settings.
You could use a molex fan, thing is, when you disconnect the Dell fan you will get a fan failure message every time you try to boot the machine.
I don't have a comparable Dell sitting here to test anything, but it should be possible to change the wiring configuration of a standard 92 mm PWM fan to match the Dell fan. I've done the opposite, reconfigured Dell fan wiring to work on standard board.
thanks guys for all of the suggestions. I actually ordered a fan from Oxide, so it should be here soon. Delluser1, yeah I already found out about the failure message on boot, no biggie though, I can deal with pressing F1 at bootup.
o1die: Thanks, I will look into the fan controller. Newegg is my 2nd home! LOL!