Font reset - possible?

I've recently just installed LOTS of new fonts that I received from work on my MacbookPro. Trouble is that they have messed up the loading of any application that uses fonts (Illustration, Word, etc), and somehow replaced some of the common fonts (Arial, etc) with something much more obscure.

Im wondering if there is a way if I can reset my fonts to the defaults that came with the Mac?

Cheers.