How much RAM can I allocate for Minecraft?

I have 1GB of RAM and I use Windows XP 32-bit, I know how to allocate more RAM for Minecraft but how much should I actually allocate, when I turn on my PC only 175MB of my RAM for system processes is used so how much can I allocate for Minecraft without having problems?

1 GB is a painfully low amount. I strongly recommend going up to 2 GB.
As it is, you barely have enough to run your system, let alone servers.

But if you are determined to torture your system, try reserving different amounts and see how it performs.

1GB RAM is not enough. Try to push to 4GB or get 2GB at the least. You have until April 2014 to ditch Xp and get a new operating system.

~good luck

You can't allocate RAM for your programs. The OS (Windows XP) does that automatically.

1GB is a really small amount of RAM even for XP. Bump it to 2GB at least for a quick performance boost overall. However based on how old your system is, you'd really be better off just buying a whole new system. Even those cheap systems from Walmart will outperform your current system by at least 100x.