In future you should save your playlists as XSPF.
As implemented in Winamp this is a locationless playlist format that relies entirely on what tracks you have in your Media Library, not where they are stored.
XSPF support can be added via the following post :
Current implementation is very slow loading, so you may be waiting around a bit if you have a large playlist and/or a large media library.
There is an upcoming release that addresses this, hopefully it will be available soon. I've found it to be up to 20 times faster.
The only drawback to doing this is that Winamp cannot save playlists in xspf format (yet??), you will need to use something like foobar to do this, (Seems fair enough, foobar users will need to use something like Winamp for content resolution). Or you may like to try the utility below.
Playlist regeneration is really just a side benefit of XSPF, the main use being the creation of shareable playlists i.e. something that can be sent to a friend and still work(always provided they have the tracks in their Media Library)
Regarding old M3U and M3U8 playlists.
While looking into this I've made a small utility that will take an M3U8 and convert to XSPF, giving you the original playlist in XSPF locationless form.
There are some limitations depending on the specific formatting in the M3U8, and might not work with all files. Not creating the <location> tag may help here.
Should do what you want, though it was originally written so as not to have to resort to some other player to create the playlists.
WARNING - It's the only program I've ever written for a Windows machine, and only ever been tested on a single XP box, so only give it a go if you think you're hard enough
I could probably add support for M3U and PLS if there's any interest.