Embedded Start-Up / Registry File? W98SE

WIN 98SE

I recently installed a shareware program for evaluation. I uninstalled the program after the evaluation period but was left with a file that I cannot locate. Now, everytime I restart or re-boot my machine, I get a text box, at the same time my Windows Logon box appears, telling me my evaluation period has expired. I cannot find any related files left to delete so I’m wondering how to access the start-up apps or registry files in hopes of locating the nuisance file. ANY HELP? Thanks!