If you don't mind switching to a non-official rom, I'd suggest flashing to either the galaxy Rom or the 1.6 Behold 2 rom that bhman released (
(Port) Behold 2 1.6 ( No Twiz w/ Busybox & Rooted Kernel ) - AndroidSPIN Forums). You could also use the Factory 1.6 rom. As far as which rom to use, if you need vibrate or the nice Behold 2 camera firmware use take5 (the final no twiz BH2 rom), otherwise use the galaxy (and if you like touchwiz, use factory). You'll find on androidspin as well (I'm not 100% on whether the current version of galaxy, r12, is on here and I know it will be there).
If you don't want to flash but want root, you might be out of luck. I don't know how you'd go about rooting 1.5 post update, and it's a good bet that the 1.6 ota will undo any vulnerabilities we're currently using. I'm guessing somebody will be able to put a rom together with the new 1.6 that has root on it.
Not to sound too harsh, but I'm sure any more questions you have will already have been answered in the root/rom/dev section, in the thread for whichever rom you decide to go with (I'd suggest galaxy unless you really need vibrate or the cool camera). And if you don't find an answer, and have used the search, you should ask there.
Good luck. It's really not that hard, and there's no real chance of permenantly bricking your phone (if you do mess it up, you can just reflash it to fix it
).