It might be wise to talk directly with Predialnet to find out if they have an anti-p2p policy or shape bandwidth at certain times of the day. It would be best to talk to a technician there rather than the people at the front desk. If all p2p programs you have tested have the same problem, then it does sound like the problem is your ISP. Ask them why your speeds should be fine for browsing but not good for p2p when there's no reason for this. Give them the example of the magnet link site. You should be able to obtain over 200 KB/s speeds downlding from there (if your internet speed can get up to that speed.)

BTW if you're using windows XP you might want to consider this patch http://www.lvllord.de/