_fastcall and _cdecl compiler options in VC ++5.0

I use MS VC++ 5.0.what is the difference between _fastcall and _cdecl options?I find my code running faster with the _fastcall option.There are no 'inline' declared functions.
I am also facing a problem with the _fastcall option.I've got a function that has a lot of inline assembly in it.When i give the _fastcall option, the Debug version runs fine but the Release version hangs! When the same function is made _cdecl, both Debug and Release versions run fine.I ahve absolutely clue of what is going on.
Any help/suggestions would be greatly appreciated.
Thanks,
Sathya


Sathya