all the cm7 roms support a2sd using the darktremor script, as well as joneidy's sense rom. you shouldn't have any problems with doing it with reppards rom, but here's some quick tips:
- go into your recovery and make a nandroid backup. after making the backup, do a restore right away to make sure the backup isn't corrupt.
- backup all the contents of your sd card to your pc for safe keepings
- go back into GNM recovery and partition your sd card with the ext partition
- once this is done (and still in recovery), mount the sd card to your pc and put all your stuff back on, INCLUDING the dark tremor script
- flash the dark tremor script as you would a custom rom
- reboot, and wait a while. This should do it.
Be sure to follow tehdude's instructions in addition to these tips; I can't remember what he said about clearing davlik cache and what not. Good luck.