Has anyone used ghostscript with php or something else to convert ps to pdf or eps?

I've not done it directly with PHP - sounds like way too much hard work. What platform are you doing this on? Windows/Unix? Unix/Linux systems may well have a program installed called ps2pdf that will convert for you. You can execute this program on the server using the PHP exec() function.

i am designing on windows but will place on a linux system for production. I am designing a site where individuals can order business cards and need to generate online image and export eps files for printing.

You can get versions of ps2pdf that install as a command line tool under windows, should work the same as on linux hopefully.

To convert ps to eps should be as easy as adding the bounding box information to the top of the file - ps files are just ASCII files so you can do this very easily with PHP. Your mileage may vary depending on where the ps file was exported from and who is going to open it, since different software packages add varying amounts of application specific crud to their postscript output.