I do not understand why you say it has to be a LW problem I run LW all of the time can play Half Life2 while LW is running I have no problem surfing the net running Office aplications, or running Adobe CS2 & Adobe photoshop3 editing photos while LW is running when I am surfing the net or playing Half Life on stream I set LW to UL 30Kb/s I really do not know what I am downloading at when gaming but I usually DL at 50 to 300Kb/s I have no trouble on my machines whitch are not that much diffrent from yours. There are times I leave LW running for days I do occasionly notice that LW is using allot of MEM 65,000K+ when running in Ultrapper Leaf usually 40,000K or less CPU usage 2% with spikes at 17% I have never seen it go above that my current machine is set up as follows

AMD 64 3200+ set at 240X10 = 2.4GHz
1 GB Corsair 3200 Value Ram 1.7v
EVGA e-GeForce 6200 core Clock 400MHz Mem Clock 635MHz
2-Fujitsu 74GB 15K Ultra 320 SCSI 0-Raid
Adaptec 29320 Ultra 320 SCSI card
120 GB WD Hard Drive
ASUS A8V Ultra Motherboard

As you can see your machine should be out preforming mine and I am having no problem with LW causing any type of lag. I did have a problem before on my other machine wit a blank screen when LW opened it has a MSI FX 5200 nvidia if I changed from 32bit to 16bit the problem would go away and and I havent seen that problem since version 4.2 I believe that LW is a mem intsive program but it is not a cripleing program in any way. There may be a problem in the way LW is set up or a driver or any number of things allot of people tend to blame LW for problems but believe me if LW is propperley set up there is no better P2P software out there go back and read some of the tips in the forum and try them it took me a while to get LW to run the way it does now and it sems that diffrent things work for diffrent people but it will be worth it if you get it set up propperley for your machine.

Latter Grandpa