how do i reinstall the os without the disk?

What OS? If at any point in time you had Lion installed, Apple allows you to automatically re-install it by booting your computer without an installed OS.
It connects to their servers and guides you through the setup. If it works with Snow Leopard, I don't know.

 

Reinstalling your OS likely won't fix this problem. What do you mean by "its hogging more memory than it should"? What version of OS X are you running? How do you know it's using more RAM than it should? What are your pageins and pageouts?

If something is really using more memory than it should, that means it has a memory leak. If the OS has a memory leak, reinstalling won't fix that, barring some sort of strange and nearly impossible situation where something in the OS corrupted in such a way as to cause that. The more likely culprit is some sort of process that is running out of control.

Unused RAM is useless RAM. Lion especially is designed to take up tons of RAM, but release it when other apps need it. It's not a bad thing, though it can look alarming.

Technically, this is still illegal. That being said, Apple hasn't actually ever gone after anyone for doing this. Logically, one would think it would be legal, but it's illegal because you're downloading something someone illegally made available. It's like medical marijuana. It's illegal (we're ignoring purity and such things) to get it from a street vendor even if you have a prescription for it.

I agree with your post otherwise, I just wanted to point out that, technically, it's still illegal.

 

Ever heard of a Hackintosh? That's not exactly a Mac platform Also, if you download via BitTorrent, you are facilitating others' downloads, and there is no way to ensure that they are downloading it for the same reason you are, which makes you a distributor of pirated software.

It's the downloading part that is the issue. If the OP's friend has a copy of Snow Leopard, and that's the version OP needs, there's nothing at all illegal about installing SL from the friend's disc.

Not interested in a legal debate either. I've said my piece, and we can leave it at that

 

Going back to topic without the illegal downloads. OP knows how to find stuff if they need it.

Anyways, I don't have a opti drive in my MBP as I am running an SSD and HDD. When I reinstalled Snow Leopard, it was a PITA. Ended up having to put the opti drive back in, then once it was installed I used Carbon Copy Cloner and cloned it to a flash drive so if I ever need to again, it's just plug and play (and pray no files get lost in the mix).

As others have mentioned, if you purchased Lion online then go that route. Otherwise, without a disk, only other way is if your friend has a fresh OS installed on a drive you could copy that over. I'd just go to the Genius Bar if you're still covered.

And as someone else mentioned above, care to elaborate on hogging up too much memory? This isn't a Windows machine where a reimage is sometimes the best solution.

 

This is why I have an external optical drive. I also have created USB install disks for all the major versions of OS X so that I don't even need an optical drive to install, just a USB port.