Are your users attempting to access the program from the server, or simply the database? I do not recommend the former and if the latter is your aim, then simply replicate all of the folders under the main ACT! folder (not the program files, just the other sub-folders) from one of the client machines to the server and map the clients to it. ACT! 4.x is sensitive to being run from a server and you can quickly run into resource issues with more than about 4 or 5 users trying to access the program. Even with fewer users, you are straining the programs capabilities by accessing from a server. Version 4.x and later are much more stable in this area than previously, but I would recommend at least getting up to v.5.04 as 4.x i no longer supported.
HTH
swk