guest OS and Mac both grinding to a halt

Of late, running Vista under Parallels has become very painful. I did not notice a specific time that this extreme slowness started, so I cannot be much of a help when it comes to tying it to any specific event. Once Vista is launched, both the VM and the Mac grind to excruciatingly slow speeds, even though there is very little CPU activity. Long ago, this used to happen on startup as the swap files engendered by Parallels' memory usage were written. Now it happens from startup to shutdown of the VM.

Parallels setup:

. build 5584
. VM set to use 512MB of RAM and 16MB of VRAM. I have experimented with setting the RAM at 864MB, but nothing much happened. The 512MB of RAM worked well in the past.
. Under the Memory tab of the preferences, memory should adjust automatically. I had experimented with setting this to manual with 640MB of RAM to no avail.
. The GuestOS is Vista Ultimate. I have not applied SP1 (which came out today). I have applied all other updates deemed to be important by M$. I have also added 2 language packs from the Ultimate Extras: German and French.

Mac setup:

. Mac Mini w/ core 2 duo running at 1.83 GHz
. 2GB of RAM
. One monitor (obviously)
. Mac OS X 10.5.2

Actions to date:

. I tried using Parallels Compressor, since it promises efficient usage of the VM. No help.
. I looked through some other threads on speeding up Parallels, and have tried the solution of uninstalling Parallel Tools (with the thought of reinstalling them later). No help.

Things I cannot do:

. I cannot try the solution of unplugging my ethernet cable, as I work in a truly networked environment.
. I would prefer not to run through the uninstall-reinstall dance so common outside of typical Mac applications. I need Parallels to test cross-platform software, so when Parallels is not functioning well, I cannot do my job properly.

What I need:

Does anyone have any tips for what could be done? I don't really care at all if Parallels is running Vista like a snail, because I can always do some other work on the Mac side.

 

Here is a partial solution with two possible explanations.

I needed to restart my Mac after installing the latest security update. Because it had been suggested on other threads, I started Parallels after rebooting. I have a fair number of startup items, but not many memory hogs.

Result: Parallels ran just fine, with all the hesitation and slowness gone like a bad dream. More than this, Parallels actually used CPU time when working. When everything was in snail-mode, the entire computer ran poorly, but very little CPU was being used.

Possible explanations:
. There were no swap files to speak of, of course, so the machine could actually work, instead of forever reading information out of swap files. Part of what was running slowly was copying a large number of small files, so perhaps the file I/O was killing Parallels, and then Parallels was killing the Mac. This explanation goes well with the original slow behavior together and lack of CPU, followed by snappier behavior and normal CPU usage.
. Parallels Tools had been uninstalled, so the lack of Parallel Tools was the reason for speed.

I've since reinstalled Parallels Tools, the VM is still working fine. Of course, this happened to others, and for some, the slowness eventually returned. We'll see what tomorrow brings.