Although it seems that the installer in this respect is a bit immature, maybe even foolish, since a 3GB RAM is more than plenty for the installation IMO. I don't think it will even touch the swap with so much RAM in hand.
As for the partitioning stuff, I think it could be the "max primary partitions are limited to 4" issue as already pointed out by Mark Phelps. But since you have wiped out windows now, I don't think it is or will be an issue anymore. If you still have doubts, please post -
..from the lappy on which you are having problems creating swap partition.Code:sudo fdisk -l