1.
Yes, if you first convert the one to the other...
2.
You can, but beware - it's no walk in the park.
If it's NTSC 24, the easiest way would be to speedup the 24 to 25 with cinematools/Conform.
If we're talking 30p or 60i....
Just to drop the clip in an opposite timeline renders bad results.
Qualitywise compressor has added some functionality from shake and shakes algorithm for th conversion. Apparently very good and veeeeeeerrrryyyyyyyy slooooow.
The next best solution - or rather best overall according to me - (and way easier) would be to buy the standards convertins package from Graeme Natress.