Gearing for Cata instances
The itemevel requirement is going to force you to gear through the ICC raid (don't do this) buy gear from the AH, or get some Cara quest rewards. I would highly recommend getting the tabards for the zones you are high enough level to get before dungeon crawling if that is your preferred method.
Level 80: Go to va'jir and get friendly and get the tabard. Also go to hyjal get friendly + tabard. Should help with item level and now you can dungeon a bit. Repeat for each new zone you unlock.
Having said that, if you choose this way you will likely have a lot of questing to go back and do for rep+ assorted other things.
I have done both ways. Neither is better/worse. Just a question of preference really. You end up needing to do it all anyways.
"he doens't need healing, he doesn't need healing, he doesn't nee-WHAOSHIT!wtf was that man!". Please stop leaning on TDR. -Teng