Apache doesn’t run on OS/400 you can run it on the IFS – what OpSys are you running there.
Yikes! V4R2 ???
For V5R4 you install the licensed program:
5722DG1 *BASE IBM HTTP Server for i5/OS
If you need just an HTTP server, then the one Voodoo mentioned above will work just fine. If you need something to run servlets and JSPs and such, then at V4R2, you would need WebSphere Application Server