What scanner resolution??

[needhelp]

Hi guys, I am just about ready to give up on my old scanner and as I dont know much about scanners or how they work.
From the fact sheet I have on a scanner I was looking at it gives the following details.. among other things of course.

Optical resolution: 600 x 1200 dpi
Selectable resolution 25-9600 dpi

Does anyone know the difference in these figures and which figure is the one I should be taking notice of in selecting a scanner.

What are the most important factors to look for when selecting a scanner..Please bear in mind that I dont have a lot of money to spend.

The scanner that I have now doesn't give me very good results on screen. I think it scans at 300dpi.
whats the least I can get away with and get reasonable results.

[sdkfz]

this should help

http://www.pcworld.com/reviews/bguide/0,guid,10,pg,1,00.asp

basically... when reading the resolution figures, note that the lower of the two numbers indicates how many dots the scanner can capture in each linear inch of the scan head (called the optical resolution). The larger number is the number of "lines" the head captures as the head scans each inch of the photo or document.

more is better of course, I know you said you did not have a lot to spend, but the microtek 6800 (set me back 400!) has a new tech called digital ice, it reduces/removes problems with damaged photographs. For myslef with a lifetime of a Grandparents pics to scan and share this is proving to me a major time saver vs manual touch up with photo shop.

What are you scanning, if text is pretty much it then a lower res would do you fine, just look for OCR (Optical character recognition) so you can scan right into a word processor. if pictures then higher is better and if you have slides/negatives then you want to make sure that the scanner can do this for you and the highest you can afford is mandatory becasue the original is small in size, and you will be blowing the image up.