I stumbled upon another trick, which applies to XP, and Vista.
With Windows XP SP2 Micro$oft introduced some new TCP/IP limitations.
With the new implementation, if a P2P or some other network program attempts to connect to 100 sites at once, it would only be able to connect to 10 per second, so it would take it 10 seconds to reach all 100.
You can check if you're hitting this limit from the Event Viewer, under System - LOOK for TCP/IP Warnings saying: "TCP/IP has reached the security limit imposed on the number of concurrent TCP connect attempts" (Event ID 4226 error). Keep in mind this is a cap only on incomplete (half-open) outbound connect attempts per second, not total connections. Still, running servers and P2P programs is definitely affected by this new limitation.
In addition, even though the setting was registry editable in XP SP1, it is now only possible to edit by changing it directly in the system file tcpip.sys. To make matters worse, that file is in use, so you also need to be in Safe mode in order to edit it.
I found appropriate patches for you:
- XP SP2 - http://www.speedguide.net/read_articles.php?id=1497
- XP SP3 - http://www.windowsreference.com/windows-xp/remove-windows-xp-sp3-tcpip-connections-limit/
- Vista - http://www.softpedia.com/get/Tweak/Network-Tweak/TCP-IP-Limit-AutoPatch.shtml
- Vista SP1 - http://www.mydigitallife.info/2008/01/07/cracktcpipsys-driver-for-vista-sp1-v668-to-patch-tcpipsys-60600117052/
IMPORTANT! You'll have to check your Event Viewer for Event ID 4226 error after every monthly Windows updates, because most likely, they'll revert tcpip.sys to its original state.

My experience
1. After installing the above patch, I have no more Event ID 4226 errors in Event Viewer.
2. Recently, I switched from BitLord to uTorrent, which increased somewhat, but...after applying the above patch....
Before, I was pretty happy with torrent speed getting close to 100kB/s. After patch, with GOOD number of seeders, I'm getting speed up to 400kB/s!.

If you use uTorrent, after applying the above patch, you have to go Options>Preferences>Advanced, and set net.max_halfopen value to 50-100. I did set mine to 80.



Good luck it worked all right then?

And I think I read somewhere that windows reserves some of your bandwidth so that it will be prioritized for the windows update downloads and therefore you do not get 100% of your bandwidth for all the non-windows update internet usage?Not correct. What Windows might do is reserve some of your bandwidth for QoS packages.
http://en.wikipedia.org/wiki/Quality_of_service
QoS packages may be used on a network to GIVE preference to certain kinds of network traffic. For example VOIP traffic could take preference over downloads to make sure downloading something doesn't disrupt a IP phone call. QoS traffic may reserve up to 20% of your network bandwidth. But as explained here it is only reserved when a program supporting QoS is actually sending something.
http://support.microsoft.com/kb/316666The whole idea came from M$ attempt to slow down spread of infection. It's explained at my first link:
Quote

In one such attempt, the devs seem to have limited the number of possible TCP connection attempts per second to 10 (from unlimited in SP1). This argumentative feature can possibly affect server and P2P programs that need to open many outbound connections at the same time.

Rant: The forward thinking of Microsoft developers here is that you can only infect 10 new systems per second via TCP/IP ?!?... If you also consider that each of those infected computers will infect 10 others at the same rate:
second 1: 1+10 computers
second 2: 10+10*10 computers (110 new ones)
second 3: 10+100*10 computers ( 1110 new ones)
second 4: 10+1000*10 computers (11110 new ones)
....
all the way to 10*60 + 10^60 computers in a single minute (that's a number with 60 digits, or it would far exceed Earth's population). Even if we consider that 90% of those computers are unreachable/protected, one would still reach ALL of them WITHIN a minute.

In other WORDS, even though it is not going to stop worm spreading, it's going to delay it a few seconds, limit possible network congestion a bit, and limit the use of your PC to 10 connection attempts per second in the process !