I just tried to duplicate your problems on this comp. for 3 hours

I'm running LimeWire Pro 4.6.0 and JRE 1.5.0_01
DirectX 9.0c

I tried to get something to freeze, and had no success.

I was running Task manager while doing this. Both left and right CPU usgae spiked then settled. With WMP the RAM usage increased. I also started a second video player at the same time.
I got the same results. My max RAM usage was appx. 900 MB at the spike.

The only time there was a change in performance is when I opened a video in MC. LW went from Ultrapeer to Leaf and I lost my connection on this browser. My d/l stayed constant and u/ls decreased. (I thought I would lose LW or crash but did neither)

All my drivers were up to date as of two days ago.

I'm not positive, but my best guess is that it is a video resource issue. LW adjusted to the various conditions placed on it.