I just got Broken Steel for Christmas. I've played vanilla FO3 twice through, the second time fairly thoroughly. Now I gather that I must complete the main quest before getting to the Broken Steel/Point Lookout stuff. Is that correct?

Should I just go straight through the main quest and then see what happens? Or should I do some of the other quests as well?

Thanks.

BS is integrated into your current game. You should have received a message that the level cap was raised, and something else, though I can't remember. Which means after clicking on that message, the game will never end, unless you start a new character. Pre-BS, the game ends after you do your thang in the purifier, but after BS installed, you will have the normal ending for FO3, slideshow (don't freak out) then you get a message saying two weeks later, and you wake up staring at a ceiling. You should have a HARD SAVE before opening the outside door to the purifier, and another before you make your decision. I mix up my quests and my exploring, for variety. A little BS here, a little PL there, a little exploring over there. Side quest or two, whatever. Just remember your hard save, as sometimes there is a glitch where you can't move when you wake up, and reloading that hard save before your decision, fixes it.

You shouldn't have to complete the main quest before doing Point Lookout. You should receive a message/signal about a boat in the river ...

After you get the Broken Steel and say if you complete the Main Quest you will wake up 2 weeks later and nothing would had changed apart from small bits and you can do the side quests which were there before you did the main quest and got killed. So you can do the main quest and not worry about losing all your side quest stuff...

broken steel is the only DLC that requires the main quest to be finished before it can be activated. the others can be started anytime you feel like it.

Don't do PL until you're pretty high level; the guys will wreck you. I went there as like a Level 25 with power armor and was horrified at the amount of damage they put out; they have huge amounts of bonus damage added to their attacks. Point Lookout is BRUTAL combat-wise, at least as far as FO3 goes.

Here's the order you want to do the DLC in:
Anchorage-Pretty much whenever, it's easy and kinda boring. You want to be a decent level with ok weaponry to ensure you survive the end though . 8-10 would probably be fine. This also gives some EXTREMELY powerful items; Chinese Stealth Armor is crazy broken.
Pitt-Pretty easy, but much more interesting than Anchorage (at least for me). High level not really needed, you fight Raiders and Trogs, both die easily and aren't a huge challenge.
Zeta-Tough, but not as tough as PL. Most things die easily, but the forcefielded aliens are very strong. Chinese Stealth Armor in particular renders this very easy as you can simply crouch in among a group of enemies and pick them off one by one.
Point Lookout-Do this last, when you are either high level or very competent with your character. Enemies are bullet/sword/punch sponges and deal ridiculous damage back at you. Great DLC, but absolute murder combat-wise if you're unprepared. This can be done at any time, but don't underestimate it like I did.

Broken Steel adds some really strong random encounters, but they're leveled appropriately, so no worries about getting owned by Albino Radscorpions at like level 15 if you rush the main quest.

Thanks for your advice.

That's not entirely true. While the quests may not be active until after you've finished the main quest, many of the features it adds will be. For instance your level cap is raised to 30 immediately and once you reach a high enough level you'll start encountering the tougher enemies it adds, like the Reavers and Overlords.

i got the game of the year edition, soooo.......

That doesn't make any difference, it's the same as the standalone game and DLCs. You might start running into some really tough creatures as early as level 14 or so. My last time through I got my butt thoroughly kicked by a Reaver down around Tenpenny Towers when I was only 14th level. And I certainly hadn't completed the main quest by then.