Comment 3 for bug 318135

If it helps:

1. Install *buntu using Wubi.
2. Install EasyBCD.
3. Using EasyBCD, add an entry for Linux>Wubi; change the drive from C: if appropriate.
4. Copy files from the winboot folder that Wubi created (wubildr*, menu.lst) to the root of the drive.
5. Go into a command prompt with admin privileges.
6. Use bcdedit to change the path of the BCD entry created by EasyBCD for Wubi from the mbr file EasyBCD installed to the mbr file you just copied to the root of the drive. (bcdedit by itself first to get the ID, then bcdedit /set {...ID...} path /wubildr.mbr)

I'm sure there is a better way (if someone could install on Vista and examine Vista's BCD entries after installing Wubi, it could help), but this seems to be a fairly quick fix/workaround.