You don't need a computer. Just copy the CM9 and
gApps (20120317 is latest) files to your sdcard via webOS or CM7 and install it from recovery. It's best to wipe data when updating from CM7 to CM9, but you shouldn't need to do it to update cm9 to a newer version of cm9.
You should be able to update via Rom Manager. Just note where you placed your files on your sdcard and open Rom Manager.
You should have installed cwm when you flashed your touchpad with CM7. If not, this won't work.
If you've never used Rom Manager before, choose
"Flash ClockworkMod Recovery". When prompted, choose "cm_tenderloin" or "hp touchpad", then "yes", and choose "ClockworkMod 3.x+".
Then tap
"Install ROM from SD Card" and browse for your cm9 file.
When prompted,
choose all 3 options (including wiping data) if upgrading from CM7. If you're just upgrading CM9 to a nightly or newer version, there's no need to wipe data.
Hopefully it'll prompt you for gApps too. If not, you'll have to install that manually after.
Here's how to update gApps manually:
http://androidforums.com/hp-touchpad/518846-question-help.html#post4103126
