I´ve been struggling with this for a while, since I´m a noob at this...
But now I´ve been able to dual boot Meego from this guide:
http://wiki.meego.com/ARM/N900/Install/Dual_Boot

Recent builds:
http://repository.maemo.org/meego/n900-de/daily/

Selet the most recent stable release of handset
Rename the downloaded file from .raw to .img and unpack with winrar or similar.(Thanks sada11 at meego.com).
Then mount on microSD with Win32 Disk Manager(see guide above).

I have kernel v46 on my device and then downloaded U-boot for kernel v46( not uboot-pr13). I had kernel v47 at first but there seemed to be som problems with u-boot and v47. I took the "safe" option and downgraded.

I had no problems with this and maybe this little guide will help other noobs

Edit: Oh well, and the usuall warnings regarding enabling extras-devel...yada yada yada