It's possible to convert bitmaps to vector formats (it's basically like tracing), but I'm not completely sure what software you'd need to use.
If you just want to have a transparency effect, or mask the image you can achieve that by using bitmaps in any half decent image editing package
If you want the editing , capabilities, and well as superior output of vector graphics you might have to resort to tracing.
BTW, vector file formats include DXF, WMF (the standard windows clipart format, but beware because windows meta files can contain bitmap information as well), and as Paul says, PSP's.
Flash files can contain vector information as well, so you may be able to get your graphics from them.
I hope I got that all right!