I don't know about those files. But I do know a little bit of Installshield 6x or higher. that can help U.
If the installation don't start or saying U have the game install. It's to thing U should look in one is regedit and one is the installshields folder. Where they place information about things. Uninstall Information is one map in program folder. My don't have any your maybe have. But don't erase anything U aren't shore of.
the second is InstallShield Installation Information also find in the program folder. (those to could be hide). Then U should have more folders with somthing about "{6BE2A4A4-99FB-48ED-AE1E-4E850389F804}" for example. Maybe the installation did a folder an put some information there. Can be so.
Well now U got a thing to look up.
Look in every folder. Look if U can in setup.ini If there is any text about Alien vs.... U know, delete hole folder. BUT before U delete. Make shore that is alien vs predidator 2 that are in the text. Second of all WRITE DOWN THE folder name.
If U find a folder with tha do like I said before then go to regedit, and search for the thing U wrote down. Second of all go to find files and mapp and do a nother search. Delete all the folders and regedit that's the "{xxxxxxxxxx}" are. Make shore that it is the right one.
IF U don't find the map there, go to temp folder and look for in every mapp, delete emptys, and look in the setup.ini files if U find the text i wrote before. Then do the hole thing again search and search in reg eidt. Don't forgett to delete those.
I'm very tiered so sory if U don't understand what U are goin to do. And I don't have the power to explain. But read what I wrote closely One rule is for shore. Make shore about what U delteing. And do notes hand writed notes about folder that U delete. Even do backups. With Winrar or somthing. The clock is 02.02 in night here so I go to sleep. Hopefoly this should solve the problem.
The things that's drives me forwad about installation problems, is how can the installation know that I have the game/software install. Well if U think about that question and U got many answer. Loock those things up, maybe that's the way installation file are looking up to know that the program/game are installed. A tip
Good night!