Easy enough, I and many others do it all the time. As long as one person is designated as the 'producer' (in other words, the one doing the mixing) you don't need to worry about plug-ins or anything else.
As long as everyone has their project set to the same BPM (or tempo map even), everything will fit together. Just make sure every track supplied starts at 00:00:00, then they'll all line up.
You can work with MP3's to start with until everyone knows what they're doing, then supply individual 24-bit tracks to the 'producer'. You do this via Yousendit, Adrive, Box.com, or many other file transfer sites.
When I collab with Bapu for example, he supplies a 'tracking shell': a .CWB file with markers for verse, chorus etc and a scratch track to work to. I record my parts against the scratch track, send him an MP3 for approval, then do it again..and again..until he's happy..then send him a WAV file.
I've been collabing with Larry Hansen in SMB for about 6 years now, and it goes pretty smoothly. We rarely have problems even though we use different DAW software to each other.