I just installed NITDroid on my N900 and formatted with gparted (on my Archlinux netbook) instead of on the N900's command line.

If you have any problems I recommend this approach instead: I have a 8Gb SDHC card and I created first the FAT32 partition with 1,9 Gb free space before it, then the ext3 partition on the remaining space.

Just a tip!