If you've got 1GB of physical RAM, congratulations! You're doing the best you can to manage your memory.

The OS X virtual memory system only pages memory to disk when it's necessary. It doesn't reserve disk space in advance, rather it grabs 80MB chunks of disk space only when they're needed.

Chances are, with your 1GB of RAM, you never have any memory paged to disk. When you use all of your RAM and the first 4096 KB chunk gets paged to disk, it will go to an 80MB swapfile. If you task the system so hard that that file is all used up, OS X will create another 80MB swapfile, etc.

You shouldn't think "I want 2.5 GB of virtual memory." In fact, you've already got that, and more--up to the capacity of your hard disk. Got 5 gigs free on your hard drive--congratulations, you've got 6 GB of virtual memory! Got 10 gigs free, you've got 11 GB of virtual memory!

I don't agree with your statement saying that "Chances are, with your 1GB of RAM, you never have any memory paged to disk".

I have 640 MB RAM (ok, not 1GB) but I still managed to create about 10 swap files (76,3 MB each) just by opening a 15 or 16MB JPEG with preview.app. other app running were : IE, ircle, finder.app, dock.app, terminal.app, that's all.

So I would say, chances are with 1GB of RAM you will have memory paged to disk sooner or later.

note that OS9 can open the same JPEG and even a 32MB JPEG without virtual memory, and it does it really faster than preview.app on OSX