I need help converting them. I love the dungeon crawls but they're all for 3rd which I don't know well (and barely any of the potential players know it.)
I plan on just using the 4e stats for the monsters but I don't know if that'd be overpowered or not. This is also my first attempt at converting anything for DnD (I've converted a lot of rules and house ruled a lot of stuff for WH40K.)
Any help would be greatly appreciated. 
Are you comfortable with editions prior to 3rd?
Not particularly. =\
I do not know much about dungeon crawls for 3rd Ed. So I cannot address the ease of converting them to 4th.
I asked because there are a few free earlier edition modules available here (www.dragonsfoot.org/ad/) for free.
Just remember when converting an encounter to make the most of the minion rules. I have converted a couple to Savage Worlds, the mook rules in SW are close enough to 4th's minion rules that I think it you should not have to much of an issue. Also pay attention to XP amounts, if after you have converted an encounter it has too much or too little XP adjust as needed. You also need to take treasure into account. Different editions deal with money and magic treasure on fundamentally different levels. So you may have to tone down the treasure in the originals.
The ones I converted were Where Fallen Jarls Sleep, and Beneath Black Towen
One thing I forgot when it comes to determining the difficulty of any encounters you convert is play-test the fight. Get copies of your player's character sheets and run the fight yourself.
To be honest I'd just start as you intended and see how you go or you'll spend forever rewriting stats. Use the 4e stats for the monsters described, just use the 4e XP budget system to make sure that everything is balanced. Remember that whilst the monsters have more powers, the players have them too.
Make sure you feedback what yuou've learnt as I'm sure there are many of us who would appreciate some feedback to help us revive oour old adventure packs. Keep of the Borderlands anyone? - sheer class.
I'll certainly share my experiences when it's all done with.
Thanks y'all for you're input! =D
One thing to remember is that earlier editions featured encounters with one room and a few monsters, tops...and often only one. Also, earlier editions keyed on the idea of attrition of resources.
So you want to look into grouping rooms together, and making encounters have multiple creatures. Try to get the spirit of the encounter right, rather than the details.
Also, as far as traps go, they're very much part of encounters now. I'd be inclined to completely remove any non-encounter based traps (ie, pit traps in hallways...needletraps in doors). Not only are they annoying and mostly just time consuming, but now really don't do anything. If the PC gets hurt by a trap between encounters, he just spends healing surges to eliminate damage. There isn't ability score damage anymore either.