How is your embroidery machine connected to the PC? How did the old PC control the machine? Did you have to install a driver or control program for it? If so, did you check to see if the company that wrote it has a WIndows 7-compatible version before buying the new PC?
Even if there is no Windows 7 program, but you used one in Windows XP, if you have a 64-bit WIndows 7 it should have WIndows XP mode and you could run the software in that.