You said you have Windows XP Professional, but then said you have Windows 2000. Do you mean you have a dual-boot system, you've upgraded from 2000 to XP, or that you have two different computers, one running each operating system?
Now, there is no SP3 for Windows XP yet...that's due out late this year or early next year. SP2 is available by going to Windows Update, but be aware it's a heft download.
When it comes to Windows 2000, SP2 was released back in 2001, and SP3 in 2002. The latest version is Windows 2000 SP4, which was released in 2003. You can download the latest service pack for Windows 2000 by clicking here.
It sounds like the installer for the scanner software has detected that your OS is outdated and needs upgraded in order to proceed. Unfortunately at this point I'm not sure what OS you're running, so we'll need to get that cleared up so you can download the proper updates.
I have window XP pro with window 2000 operating system.
trying to installed a Umax Astra 2100U scanner, I got a
note, that I should upgrade SP2 to SP3 inorder to com-
plete entire software installation. Please help