ROM Manager is horrible for the Optimus S. The stickies at the top of the forum try to alert new users to that in big, capital letters.
GOO Manager actually works IF one has the correct recovery options on their phone. I think that it can be used with Cannibal Open Touch, and with one or two other custom recoveries for the OptiS. What it does, however, is lets you find a ROM that one of the OptiS developers uploaded to Goo.IM, lets you select it, then itself kinda accesses the recovery, backs up, wipes, flashes, boots. So . . . it's a bit like a script, and in a fair number of cases you're better off NOT using its "dumb" options. Some ROMs require you to wipe a few more things than the norm.
You really should take the time to do it the long way around. It's darned simple, and the difference is about the same as pressing "1 3 0 Start" on your microwave instead of just pressing "Popcorn". Popcorn button will often work, but if you need to change anything about the way it works . . . you can't.