To do screengrabs on Mac OS X, you'll need to use the feature known simply as Grab.
No need to download it from any websites, as it comes with Mac OS X as standard.
The Grab program saves all screengrab images as TIFF files, so you'll need to open
your screengrabs in a suitable graphics manipulation app, and save as PNG or JPG.
On another subject, you might want to consider upgrading your internet browser.
Microsoft discontinued IE for Mac last year, so there'll be no further updates for
it beyond v5.2.3. I'd recommend using either Mozilla, Netscape or Safari as the
primary browser on your Mac, and put IE to one side as a seconary browser,
to be used when you visit a site that foolishly blocks all non-IE browsers.
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.2) Gecko/20040804 Netscape/7.2 - DJGM.co.uk (ax)
SeaMonkey = Swiss Army Knife: It's versatile, reliable, and contains useful tools.
Windows Internet Explorer = Old Swiss Cheese: Full of holes, and it stinks!