If you run out of virtual memory by default XP should automatically increase it for you. But you may also have it set to custom with a max amount of RAM set in which case Im not sure it will still do this. So first I would check that. Right click on My Computer, go to Properties, Advanced tab, settings button for performance, Advanced Tab again, then finally the change button for VM.
So by default this would be set to System Managed size. When its set to this, XP will create a pagefile which is your VM. The only disadvantage to this is if you use all of it up, XP will have to increase the file size and therefore it will cause your system to lag. But even then it should rarely have to do this unless youre always running allot of stuff.
Now if you see that it is set on custom just increase the size. Or if youre not comfortable with that just set it to System Managed size.
As far as your network goes, I dont see any reason why it should be exhausting your RAM anymore than all the other things you have running. You may just need to reboot to free up some RAM that has been used and not recoverable. Theres also a program I use called memturbo that will do this for you without having to reboot.
Besides all of this, if you find yourself constantly running out of VM that means your using allot of it. And if you are youll notice a huge overall performance increase by adding more physical ram. When a system runs out of physical RAM and has to start using VM it will start crawling no matter how fast the CPU is.
Sorry that ended up being so long winded. Hopefully it made sense.