You can probably pick up a *cheap* copy on eBay, at a Car boot or at a local Computer Market..
You may find that older versions (probably v4 or 5) are available free with some Computer Magazines.. I know this to be true of Paint Shop Pro..
As for a Free Photoshop say CS2, you're gonna have to resort to criminal activities.. and unfortunatley we can't condone this on AB. I'm sure a quick Google will give you some results.
You used to be able to get a watered down version of this with some scanners. Photoshop has really gone down in price. Eaby would be your best best. Even though it is illagal and not something I would condone, you could always search using peer to peer software like Limewire, Imesh or Kazza. I stress that that would be illegal.
Recent versions of Paint Shop Pro do everything that Photoshop does and seem to be much lower in price.
Also there are free programmes like Gimp which offer LOADS of features for a free download.
There's no such thing as "photoshop for free" unless it's illegal.