Weird crash and memory

I've been using PD4 on and off for a week or so and have been impressed with the general improvement; prior to the upgrade neither PD3 nor Fusion did more than stall my system and cause endless frustration, to the point where I simply uninstalled both and used Boot Camp exclusively which somewhat restored my peace of mind, but the tedium and inconvenience of either/or was almost as unsatisfactory.
Last night something weird happened. I'm no sophisticate, so what I'm about to recount may not qualify as weird, but I'm nonplussed.
Anyway, soon after upgrading to PD4, in anticipation and for other reasons which will become clear, I upped physical RAM from 1GB to 2GB on my first generation intel iMac. It is not unusual for me to run Safari with a few tabs; Mail; and iTunes, and another application or two as well, which was the case last night also. In addition to that, XP had Chrome running, again with a few tabs, as well as Explorer and in the middle of that XP decided to do a disk cleanup. I guess it's no surprise that both systems froze: both the keyboard and mouse were inoperative, though the alert chimes for Mail and Google Notifier were still audible. I waited a while: made a cup of tea, but the freeze seemed permanent. So I did a hard restart, restarted PD4 which seemed oblivious to the earlier shenanigans, and things have been as usual before the weirdness.
I guess I'm overloading the system, for instance, even without the plethora of applications running, initially PD4 is agonisingly slow, but it soon speeds up and even so, it is a much better alternative than booting in XP mode only, I did after all buy an iMac to use as Mac, not as a Mac that can run XP.
I do have some questions though. Do I allow PD4 to dynamically allocate the amount of memory it needs, which is what I allow at the moment, and which I surmise could be the cause of my problems: as I run more and more applications, especially of the XOS side, the amount of memory available diminishes and consequently the events of last night. Or, should I perhaps allocate it a fixed amount of memory? PD4's default setting is around 600MB, which is well over what PD4 dynamically allots itself and it is certainly well over what any other application seems to need, even Safari which truly is a memory hog doesn't approach much more than half of that. I think I've correctly diagnosed the symptoms and the cure is self-evident. But any advice you can offer would be appreciated.
I use PD4 for very low level stuff, nothing too intensive, and I'm not likely to in the near future, I suspect that once I upgrade my current machine to one with more RAM and faster processors then my minor travails will evaporate.

 

Hope tips bellow will help
1. Set memory for Virtual Machine to less than 1 GB for Windows XP , and more that 1 Gb for Vista
2. Perform Mac and Windows side disk defragmentation http://www.xvsxp.com/system/system_tools_defrag.php
3. Set Adjust memory tp Auto from Manual at Parallels Desktop -Preferences-Memory
4. Disable Themes in Windows XP serives.msc stop Themes service
5. If you are running in Coherence, try to switch to Single Window, or lower Mac resolution
6. Some antivirus software can load CPU when Heuristic Prediction is set, or Tamper protection (Symantec, MacAffey), adjust settings to risk you are supposed, high security settings is not always good idea, as it can also affect software running
7. Run msconfig , and disable unneeded startup items
See http://www.netsquirrel.com/msconfig/msconfig_xp.html
8 Optimize computer experience for best performance
9. Make sure that at least 1.25 GB of Memory is free for Mac OS (it is Total Memory - Virtual Machine Memory)
10. Make sure that at least 2 GB +Virtual Machine assigned memory *2 is available on Mac OS partition where VM is located

 

Thanks for the tips, some of which I've implemented: PD4 now seems more stable and faster, well, eventually. I've only got to 2GB of RAM, Leopard is pretty hungry most of the time - especially Safari. Yes I know I could turn Safari off, but that sort of defeats the purpose: I use Spaces a lot, I rarely use Windows exclusively - if I did I'd use Boot Camp anyway -, so, having a few apps running is something PD4 has to accommodate, which for the most part it does. I'm happy with it at the moment.
But a couple of questions:
(1) Windows is forever telling me that disk space is low and whether I'd like to free up some space. I do, of course, but I have 38GB free, I don't see how it's running out of space.
(2) This is trivial, but when I go to full screen mode the set transition effect (cube, flip, wipe etc) doesn't show, instead it goes straight to full screen with a boring super quick dilation Any suggests how to get a cool transition to work?