A "Non-system disk" error is a classic WIN9X message that indicates the boot loader file is missing. In WIN9X, the boot loader file is io.sys. However, if the boot loader for WIN2K is missing you should receive a different error message: "Ntldr is missing or corrupt"
Either you have botched a dual-boot installation, or you are posting incomplete (incorrect?) information. In any case, Victor's suggestion that you reinstall WIN2K is appropriate. OR, you could make an ERD with the WIN2K Backup utility and attempt a repair. A complete data backup and reinstall would probably be your best option.
Installing WIN2K can be a bit tricky the first few times you do it, especially on a laptop, because there are many different options for partitioning and file system combinations. You may want to go on line, or get a book and read up on it.