SP2 breaks TCP/IP intentionally by limiting the number of connections that can be waiting a responce from the other end. If the host its connecting to is down or the packet gets dropped, they can sit like this for a good few seconds. Doesnt take many before your machine starts filling the event log with crap about reaching the limit and apps start to misbehave. It affects everything, incuding the ability to access shares.
At the end of the day, I couldnt reliably run any p2p apps on SP2, they would keep losing access to the shares with files on, and transfers would often fail to start. going back to SP none (Thankfully I ghosted before installing it) and the problems went away.
It really annoys me that MS can take away functionality in something that I have bought in the disguise of it being a securty feature.
Are you talking about QoS? If so, (a) that's not how it works and (b) it can be disabled.
And really, REALLY seriously, if you are actively downloading content from P2P without any service packs, you are asking for heaps of trouble. It's a ticking bomb.
Try SP2, allow all P2P specific tcp-port connections through the firewall (or turn it off al together and use a standalone firewall/router with proper port forwarding) and ensure you have QoS TURNED OFF.
I build large networks for a living, as well as contract out to home users on the odd occasion. In EVERY SINGLE INSTANCE where I've helped home users with home networking and P2P setups, it has been a misconfiguration on the user's behalf that has limited functionailty. There are plenty of FAQs on P2P sites (the BitTorrent places are usualy VERY friendly and have plenty of info) and these will get you running at optimal speed, even with P2P.
I download all of my Linux ISOs through Bittorrent. My dedicated Bittorrent machine is a WindowsXP SP2 box sitting behind a Linux firewall. I ALWAYS get full speed torrent downloads with no hiccups. If you have issues, I say again: IT IS NOT SERVICE PACK 2. It is your setup, and you need to configure it correctly.
My configuration is as such:
1) On my standalone firewall (running Smoothwall Linux), I have all TCP information on ports 6881 through 6889 unblocked and forwarded to my BitTorrent downloader. These are the standard communication ports for torrent, and if blocked will result in your torrent speeds capping themselves at very low levels (usually around a few bytes per second). Other services will use different ports, and you need to look these up.
2) Internally my torrent machine has it's firewall turned off. I consider my LAN secure, and protected by my edge firewall device. If you have users on your LAN who you don't trust, you may need to trun this on, and allow exceptions for ports 6881-6889 as before.
3) The torrent machine has only standard TCP/IP networking enabled, and QoS TURNED OFF. Other than a vanilla WindowsXP SP2 install with all of the latest updates applied, the only other security software is a copy of Grisoft AVG Anti-Virus (free for home users), which is set to realtime scan, as well as update daily, and do a complete system scan at 3:00AM every day.
Follow those basic steps on your network, and I can guarantee you'll see full speed on your P2P downloads, even with SP2 installed.