I am not a CPA or an attorney. . .
As you are beginning to go back and file your returns keep in mind one thing. . . the tax agencies are MUCH more lenient on you if you file your current ones. I would put emphasis on getting 1999 done ASAP and do not even file for an extension for 2000. . . get it in as soon as all of your information is accessible.
As far as the old returns for federal and state, I think that after 3 years you can no longer get a refund, but you can still owe the tax. . .just like the government
I do believe that even if you are filing a return that has a refund that you will be penalized for forfeiture, filing late, and interest on the penalties. BUT, they might pay you interest on the refund.
If you have the funds, I would consult a CPA in private practice. He or she could help ease the burden of finding the old forms and contacting the agencies. Despite their bad rap, CPAs are funny people. They are just misunderstood