An old inspiron you say.
don't buy from the dells home site. those CPU's used for there socket T is expensive.
back when your machine was launched, Dell had renamed the socket LGA775 to socket T.
that is to confuse costumers into buying from DELL directly. i had that problem with my DELL Demension 5000. Back then i was not so much into computer as i am today. so i called DELL to hear what CPU i could get as an upgrade. they showed me some WAY TO EXPENSIVE cpu's with the socket T. i search for a cheaper socket T CPU, but didn't find much outside DELL's homesite. so i gave up.
I later on figured out that it was just a LGA 775 socket.
It's just typical DELL. they are getting better now, but they have been some assholes.
they once had there own RAM's, and there cases only support there own PSU's.
DELL are also the inventer of the BTX formfactor.