flashing the roms is a bit outside the scope of this thread,there is lots of info on that if you search thru the forums. if you want to link a couple guides youve found,we can comment on them in those threads,and if you start a new post in the forum,youll get lots of good advice from knowledgeable members that just arent seeing your questions in this thread.
in a nutshell,you will download the rom you want to flash. with cm7 you will also need to download a second file to flash,called "gapps". gapps is simply googles proprietary apps that are not legally allowed to be included in the cm7 rom. if you dont flash the gapps right after flashing cm7,you wont have the market,gmail,or a couple others.
-download cm7 and gapps
-place them both on your sd card. do not unzip.
-boot to recovery(power off,power on to hboot,chose recovery. or use an app like "quickboot")
*using recoverys menu options(been awhile since ive used clockwork,so i dont remember them exactly):
-make a backup of your current setup
-wipe data/factory reset
-wipe dalvik cache
(ok,those last 3 were from southpark,so dont do those
) but the rest of it is a basic outline of what youll do. when flashing the zips,no need ot rename them "update.zip" there will be an option to "chose zip from SD card" so you can just find your zips and flash them.
so if you still have some questions,direct us to some new threads,or start up your own new thread and well be happy to continue helping
the best advice i think you can get as a new rooter(IMO,at least) is DO NOT
use rom manager. it is known to eff things up,and when it does you will have to have the knowledge to fix them manually in clockwork recovery. rom manager is an APP in a WORKING ROM and as such,will not always be available to you to use. it is much safer and reliable to manually manipulate things in clockwork recovery.