If your needs aren't too complicated, you could try IrfanView click here
If you want something as capable [and complex] as Adobe Photoshop but don't want to pay for it, The GIMP is a superb program but takes alot of getting your head around. Originally coded for Linux it has been ported over to Windows and you can grab it from click here
Manay magazine covermount disks feature older versions of image editing software.
If you do decide to buy one product, you'd be hard pushed to find something better than Ulead PhotoImpact. It comes in at a very reasonable price, has a very wide range of features and is also far easier to use than many other editors.