Most newer digital cameras come with a usb adapter. If running XP then no software is even necessary as XP picks it up and lets you transfer pics to a folder very easily.
One big thing to keep in mind if you want zoom. <b>Optical</b> is true zoom, forget "Digital" zoom. "Digital" zoom is completely worthless and a cheap sales technique camera makers use to make people who don't know any better think they are getting a zoom lense. All digital zoom does is enlarge the center of a pic, same thing you can do with any decent photo editing application. And that makes you lose quality. Optical zoom is true zoom and with that you don't lose nearly as much quality.
Other good things to have is a flash, optical viewing lense (so you don't have to rely on a lcd screen only), self-timer, macro (for closeups), compact size and the ability to use AA batteries. Using AA batteries allows you to use rechargeable nimh batteries. In the long run using nimh batteries will save you moola, plus they last longer than alkaline batteries. I mention a compact size because I've had several digital cameras and when I had a larger one I didn't carry it with me as much as I do with one pocket size.
Most digital cameras use either smartmedia or compact flash for the memory stick (where pics are stored). Both go at least up to 128mb and that's more than enough for most people. But most cameras come with a small 4-8mb card so you'll need to get another card eventually because with a 4-8mb card you can usually store around 6-12 pics. Good place to get memory cards is
http://www.newegg.com. Both are good media and about the size of a matchbook, smartmedia is thinner and while compact flash is a bit thicker.
Most newer cameras have the options I mention above, but not all have optical zoom, if you want zoom anyway. Check out some reviews I've done on our news page for sample pics, the pics were all taken with a ricoh rdc-4200 (earlier reviews), fuji 1200-1300 and a fuji 2300 (most recently). The pics looked better before I resized and compressed them for a web page of course.
And yes, usually the higher reso the better quality. But that also depends on the camera and the lense. With your budget of $300 you'll be able to find a good one easily. Check the sales at places like Compusa and Best Buy. Sometimes they have good sales on digital cameras and include a larger memory card and other assorted goodies.
I'm not up to date like I use to be with the latest digital cameras but check out these sites and read reviews on any you may be considering.
http://www.steves-digicams.com/
http://www.dcresource.com
http://www.megapixel.net/
For nimh batteries and a charger I suggest
http://www.thomas-distributing.com/batteries.htm
Or a local Costco or Sam's Club usually has an 8 pk of AA nimh batteries 1600mah with a charger for 19.99. Higher the mah usually the better and they last longer.
*One real cool thing I discovered by accident is the last few fuji cameras I've had can take a good pic in darkness, when using the auto or forced flash. Everything is in focus just fine. That still amazes me. *&
Hope that helps
