How do you optimize screenshots?

I produce short online guides for internal employees and I'm having a difficult time with my screenshots -- they come out blurry and sometimes illegible. How can I capture and manipulate my screenshots so that they look good? My priority is esthetic quality; file size is second.

I've taken them on a PC, on a Mac, on a laptop, on a 30" LCD monitor. I've adjusted the resolution on my monitor. I've used the "+" feature in Firefox where you can increase the image size of your web page. I've "Saved for Web and Devices" in Photoshop. I've seen tutorials with clean/crisp screenshots so I feel sure this can be done.

My typical workflow is that I build an InDesign document (with Web settings @ 800x600) and export as a SWF.

i don't understand how a screenshot can come out blurry?!
i take it you mean AFTER resizing them? have you tried converting them to a smart object? the only other way to minimize this is to save the screenshot, adjust it's properties to a far higher resolution and then try resizing them.

It's only after I build my document and export it for online use (as a .SWF) that they are blurry. Within my InDesign document they look pretty good. I'm also very aware of resizing -- rarely do I increase the size of anything. Most cases I am decreasing the size.