You didn't save your JP when you leveled?
More importantly, why weren't you capped from farming Wotlk five mans before cata hit?
I registered on MMO-Champion and all I got was this lousy signature.
I'm a cynic. Deal with it!
How to enter heroics - quick guide:
General rule (apply this to every step): for every slot you have you need an item with level above 329 equipped or sitting in your bags, no matter if you can wear it or not.
Step 1: During last 2 levels (84 & 85) try to get every item with level 333 and above from quests. If you cant use it (you are a priest and the item is mail), its OK, just keep it in your bags. Try to have items for as many slots as possible.
Step 2: Level up to 85
Step 3: Buy any item with JP with level 346, preferably for slots you don't have quest items for
Step 4: Scan your gear + bags: if you wear a green item level 281 and you have an item with level 333 in your bags, then its all fine. If you don't have higher iLvl item in your bags, then a) go see the quartermaster(s) of the highest reputation(s) you have after leveling and buy whatever is available or b) go to AH and buy any crap that has 333 on it (no matter if you can use it or not). Remember General Rule.
Step 5: Clear your bags of all low iLvl crap (i.e. all below 329)
Step 6: Press "I" and join queue for Random Heroic Cataclysm Dungeon.