I've got an ants nest in mine too. I don't have a problem with it as they are aerating the compost but aparently its a sign that the compost is too dry or has too much brown stuff, which I know mine has cos I dug up my 'lawn' complete with a lot of soil, then got a compost bin and slung the lot in. I've started to add a little bit of kitchen waste to the compost bin now so it should eventually balance out, then the ants will take themselves off somewhere else. I try not to interfere with them as they have a lot of eggs and are obviously happy there (and I'm happy they're not trying to get into my kitchen). Anyway, you could have a look at these links:
Recycle now - Compost Bin Issues Camden Council: Composting
I suppose it depends on how patient you are about getting your compost right. Personally, I'll let nature take its course for a while.