If by some miracle you were able to get MS SQL 7 to run under Linux, why would you want to? There are several good RDBMs systems native to Linux which will be much faster than MS SQL in a simulated windows environment.
Leave MS SQL on a windows NT box. Put PHP on that box, or better yet, separate the Web server and DB server (but connect them on a fast network). I use MS SQL on one box and reach it with PHP from both IIS and Apache boxes (both Linux and NT).
BTW, Samba is an implementation of the Server Message Block (SM😎 networking protocol used by "Widows Networking". It has nothing to do with the MS Windows API (except where there are special API hooks related to SMB networking). You can use SMB networking between two Linux boxes if you want (kind of like TCP/IP). These days, you usually see SMB over TCP/IP. Occasionally you still find a SMB over NetBEUI. (Those were the days!)