I'm not really into diesels, i own a nitro truck but could you guys tell me a little about them and what the diesel engines are in (cars, trucks, etc) and where to buy them?

Stock "out of the Box" RC car and truck diesels at this point do not exist. With the large increase in intrest in them same reason as planes increased torque and fuel economy Davis Diesel (the same guy who makes the conversion heads for planes) has started
making them for this use your best bet is a call to 203 877 1670 martin

if i wanted could i convert my traxxas trx 2.5 to a diesel?

"if i wanted could i convert my traxxas trx 2.5 to a diesel"
Yes -------- BUT!!
the converted motor (any diesel ) in your car will need a bigger flywheel( heavier clutch assy), or starting will be very difficult and the idle will need to be much higher , this is due to the higher compression of a diesel. It will also need the gear ratio of the driveline changeing to get the advantages of a diesel.
This is no big deal with aircraft as simply useing a larger dia prop will acheive this, a larger prop also makes better use of a diesels higher torque.
This is not to say a diesel cant be run at the higher RPMs like a glow. The MVVS 15 is a good excample, to quote some No's :- " According to Aeromodeller review, Aug, 1997, peak HP 0.56 at 20,000 RPM,
Peak torque at 17,000.
Recommended prop 8 x 4 or 7 x 6. Without silencer, 8 x 4 APC turns 16,200,
APC 7 x 6, 16,500. 9 x 4 APC 13,100."
Also one of my favourite small diesels is an 1970's 1cc Barbini, this was designed for both aircraft and tether car use, it swings a 7X5 wood zinger prop at or above 11,300 RPM But max HP is at 18,000RPM and Max RPM's are 28,000, both good examples of a diesels flexability.
Stewart

hmm... would i get the same preformance and what would it cost to do

Ryan,
An educated guess , I would say your max rpms will be slightly lower, but the acceleration will be better (due to higher torque).
There seems to be very little first hand experiance with R/C diesels in cars, so you may need to do some fiddling with setup to maximise the installation. There was a guy last year useing a diesel in tractor pull models , do a search, maybe exchange a few emails with him.( sorry no link )
Stewart