In the prior versions of Movie Maker, the audio would be retained.
In WMM 2.x (either 2.1 from XP or 2.6 from Vista), the sound will change pitch. In other words, if you slow it down you'll get lower pitch audio. If you speed it up you will get "chipmunk" audio. So if this is what you want, follow PapaJohn's advice to download WMM 2.6.
In WMM 6.0 (the full Vista version), the sound will not change pitch. It will speed up or slow down (e.g. slower or faster speed) while aiming to retain the audio pitch as much as possible. So if this is what you want, consider installing WMM 6.0 on Windows 7.
The last option is to extract your audio from your video file, then use an audio editor (like Audacity which is freeware), to speed up/slow down your audio by the corresponding amount. Finally manually add it back in as your "added music" track where you are speeding up/slowing down the video. Audacity has options to change tempo and also change pitch or instead change tempo but retain pitch. This is an advanced method and will require some conversion (e.g. ability to extract only the audio, change it in Audacity, add it to WLMM and resynch it, etc.).
So take your pick of workarounds. If you'd like to suggest this as a feature in WLMM, go to the feedback.live.com site.