The new ROM Manager now support SD card partitioning. You will also need to flash one of bekit's V0.8 kernels.
Start up ROM Manager.
Flash the newest recovery if there is an update..
# =====The next couple steps will not be necessary soon.=====
Make sure you have Developer mode on.
Go to the CyanogenMod download section.
Install one of bekit's V0.8 kernel. Choose "Stock" if you are unsure which to pick.
After the phone reboots, start up ROM Manager again.
#=====end of soon to be removed steps.=====
Choose Partition SD card.
Choose your ext and swap size (or choose the defaults if you are unsure).
After the phone reboots, go into Settings -> Applications.
Note: Nandroid in ClockworkMod recovery does not support ext backup yet. Coming shortly.