Break it into pieces. Copy and paste parts of the timeline into new projects, export them separately to "high quality large", write an avisynth script to open each one in VirtualDubMod using the directshow filter and 29.970 fps, convert each piece to huffyuv in Vdub, open the first huffyuv piece and use the 'append' option to open the next pieces in the proper order, reattatch the mp3 file and compress the footage to xvid 1st pass. If it looks fine, you're set. If it looks fuzzy, try adding a filter or two to your avisynth script. If the file's too large, run xvid again and use 2nd pass or lower the resolution in the avisynth script to 480x352.
Or you can import those wmv pieces back into wmm, slap them on a timeline with the audio, and export *that*. Your quality will suck big time, but it's an option.
Get amv-app if you don't have Vdubmod, huffyuv, avisynth, or xvid:
http://www.animemusicvideos.org/guides/ ... mvapp.html
Check this guide to learn how to use those programs and codecs:
Read the bolded "sticky" thread at the top of this section and remember the flashing rule of thumb - don't edit with compressed footage (that's divx/xvid, mpg, wmv, and so on). Only use huffyuv or lagarith. The next time you use these clips, convert them to huffyuv first. Just because wmm let you use them once doesn't mean it'll do it with any consistency.