Since the beginning of personal computing, users had to prepare the printing of data files on computers when the printer was not present, not connected or not available. The solution in this case is to print to a file. In the printing dialog box, you can select "FILE" as outport instead of COM1, LPT1 or the like.
In this case, the printer program sends to this file (which bears most of the time the PRN extension) all the commands and data which would otherwise go directly to the printer.
This print file, which you can consider as a program, can naturally only be used with the printer for which it was composed.
As Postscript is a printer command language, the files produced by the printer program are more generic and can be used on almost all Postscript printers if you use classical paper formats.
In the case of RIPs, things become more complicated, since the resolution and film width can vary a lot. As a matter of fact, you can install on your computer the printer your Service Bureau will be using.
This solution can be the only one when the front-end computer of the RIP is not the same as yours: e.g. you work on a PC and the SB uses a Macintosh computer as front-end to the RIP. This way, you avoid all format transfer problems, most of the font problems, etc.
A Postscript print file created on the Macintosh with the LaserWriter 360 engine bears the signature "TEXTvgrd".
Xpress goes a little further. When you print to a Postscript printer, you can choose in the Options property page the precise model of your RIP if you have the PDF/PPD file for it (those files should be stored in a subfolder called PPD or PDF in Xpress' main folder; if there is no PPD subfolder, juste create it). In this case, you will only have to specify the parameters that can change for the precise model you are using.
If you don't have the PPD/PDF file for the RIP your SB will be using, you can also select the generic B&W printer. In this cas, you will have to specify at least the film width and the resolution.
You should first ask your Service Bureau for the characteristics of the RIP it intends to use for your job. Maybe the SB will be able to give you the PPD/PDF file. Some will rise technical and/or legal issues. You can also visit the Web site of the RIP builder. More, Adobe offers on its Web site the PPD/PDF files of several printer models.
If users of SB have many horror stories about the treatment given to their jobs by some SBs (more or less competent), the SB also have many cases where they can correct silly mistakes at the last moment. If you want to go the [PostScript] print file route, you better add some checking before sending the files.
One good solution is to use Acrobat Distiller. Its price is low enough to allow a professional user to buy it without any hesitations. As this program is a Postscript interpreter, if it doesn't choke on your print file, you can be reasonnably sure that the films you'll get will conform to your expectations.
Anyway, I recommend you try this solution with a little, non urgent job. Don't put in the balance a big job or a deadline which could cost you your job or a major customer.