If your laptop is on the network, you don't need tversity, do you? I know I'd rather stream the file itself to a machine that can read it, and not an mpeg2 transport stream or whatever tversity uses to convert to, but this would depend on your wireless connection performance if you're planning to share 1080p files and you want them down-converted for streaming.
As to your tversity question, I think this thread might have an answer for you...it seems as if Win7 and Vista use SSDP discovery, and you may have to disable that to interface with an XP machine for tversity, to enable it to see all your movies/whatever:
Providing you have good wireless performance or a wired connection and have access to the software, Win7 Media Center (along with free Media Browser plugin and whatever that other plugin is that goes with MediaBrowser and makes it easier to update metadata), does a great job, as does the "libraries" feature in WMP, if you want something even simpler or if you don't have a Windows version with Media Center (Home Premium or Ultimate). I'm using MediaBrowser for all my TV show / Movie streaming and cataloging needs, nothing could be simpler, and it looks great with all the automatic backdrops for your series/movie folders, program info, etc. Once you have, for example, a folder for a TV series with a folder for a given season of the show within that, it automatically adds a wallpaper/backdrop/banner/thumbnail for each individual episode...just drop your torrent...er...file into the right folder and it does everything else. It's all free, and takes very little time to set up. I don't know what Win7 Media Center is like when it's pointing to a shared folder in XP, but I would imagine it would be the same.
If you don't have access to Media Center, I would suggest looking into Media Portal, which has similar plugins and such available, but the setup can be a little more daunting. Nothing to write home about, tho, wrt difficulty.