I know I had some trouble just getting past the basics... once I got started, it all added up. Although it seems dumb now, here are some things I didn't get that are obvious once you get moving, but that people assume you know from the get go. The links above are great as well..
Basically after rooting, I downloaded ROM Manager. From there you can flash a recovery. It may not show up at first, but after a little bit of time, you should see a recovery under the flash alternate recovery option. It should be version 1.25 now I think. What this is doing is taking the stock recovery (basically what the phone uses if your phone gets hosed and you reset it to stock) and replaces it with a custom one that has the features you'll need for changing roms. You then reboot to recovery. My recovery wouldn't stick, so I had to flash a file that I believe drellisdee provided on here that forces it to stick. So the process was to put that file on my SD card, go in to ROM manager, flash the alternate recovery, boot to recovery, immeadiately flash that file using the flash from SD card in recovery option, and then boot the phone. Now is a good time to do a nandroid back up as well... this is also an option when you boot to your custom recovery. Anytime you want to boot to your custom recovery menu, you just power the phone off, power it back on, and hold send, off, and menu at the same time. At this point you have a custom recovery and the rest is basically following instructions in the thread of the ROM you want.
I've personally had amazing results with the new punisher ROM. I love it. Everyone has their own opinions, but its my personal favorite, and its extremely easy to use and flash... just make sure you follow the directions, back up your data, back up your SD card to your computer before flashing and partitioning the SD. Once you get past that first step of flashing the recovery and knowing what that means, everything else has been made simple... just remember to do nandroid backups before doing anything.
http://androidforums.com/getitnowmarketing/146564-ally-recovery-img-here-custom-roms.html
That above link has the recovery kill file you'll need if your custom recovery won't stick. Save signed_kill_install-recovery.sh.zip to SD, flash the recovery in rom manager, reboot to recovery, flash the file from the SD card, and enjoy.
Also, remember to donate to the people that are putting all of this work in to these phones. Donating is easy through paypal, and most of the people have links in their posts. They derserve it!