Okay, you have the sweater body on one circular needle, the sleeves on holders. Knit the sts across the back or front of the body, then knit the sleeve sts off the holder, knit the other half of the body sts, knit the other sleeve sts. It's going to look weird, but after a couple rows it will start looking like a sweater. The next round after you join the pieces is usually a decrease round where the sleeve/body sts meet, that helps anchor them together.
sue- knitting heretic