The Y2K issue has two areas of concern: Hardware and Software.
HARDWARE For Macintosh Computers: ALL Macintosh computers ARE Y2K compliant. For PC (WINTEL) Computers: If your system is older than a Pentium computer (e.g., 386 or 486), most of these computers ARE NOT compliant. There are even some Pentium computers that are NOT compliant. For these computers, you need to run one of the many (some are even free) Y2K check programs. These programs check the BIOS and the Real-Time clock for errors in reporting dates for the year 2000 and beyond.
SOFTWARE This area concerns both machines, Macintoshes and WINTEL PC's. The software area of the Y2K issue also has two areas of concern. The first is pre-written software like Microsoft Office (e.g., Word, Excel, Access and PowerPoint). The second area of concern is custom databases (DB), spreadsheets (SS) and/or programs.
For pre-written software: you need to contact your software manufacture (e.g., Microsoft). In most cases the "fix" will be upgrading to the latest version of the software.