Vista - Old computer being used as an traffic encrypter?

So, I've got an old computer that still works but is doing nothing right now and I'm wondering if I could set it up so my router goes to it, which then goes out to my network.

Router > Old PC > Switch > Other PCs

I'm wondering if I could put this old computer to use encrypting my internet traffic just for the hell of it. So that anything that comes in gets scanned, or whatever so I'm very well protected and then anything I send out gets encrypted so that no one knows about my traffic but me. Should I attempt this or would it be violating some hidden terms from my ISP? I just mainly wanna do this because, well, I'm bored as hell and have nothing better to do with these few computers I've got just laying around.

The old computer is an AMD Duron 1.2ghz, 512mb RAM, Geforce 6200gt video card.

Encryption requires something else at the other end to decrypt the payload. It's no good having the strongest encryption algorithm on Earth if the internet server which receives the (encrypted) request can't decrypt it in order to understand it.

Odds are you already use encryption in the right places - every time you do your internet banking via the bank's HTTPS site.

Yea I know about the SSL stuff for online banking, etc. But I'm just wondering if it would be troublesome to encrypt everything from random surfing, downloading, etc, etc. But yea I was thinking about the decryption of it, so I guess I'm out of luck.

Any other ideas I could do to put this old pc to use again?

Do you use torrents? How about a seedbox?