Please can you help me with this translation? I amstuck on the
technical expressions!

Beim Gegengeschäft sind wir aus mehrwertsteuerrechtlichen Gründen
gezwungen, Ihnen oben aufgeführte Leistungen in Rechnung zu stellen.
Das Gegengeschäft stellen wir Ihnen mit einem fiktiven Wert von CHF
1'000.? plus MwSt. in Rechnung. Im Gegenzug senden Sie uns eine
Rechnung in der Höhe des gleichen Brutto-Betrages inkl. MwSt. in
Schweizer Franken. Jede Faktur ist innerhalb ihres Zahlungstermins zu
begleichen. Ausnahme bildet das Gegengeschäft bei Publikationen
ausländischer Verlage: hier werden die Rechnungen gegenseitig
ausgebucht. Zwingend ist, derselbe Brutto-Betrag inklusive dem
jeweiligen MwSt.-Satz zu fakturieren (CHF 1'076.?) und die Rechnung
mit «bargeldloses Gegengeschäft» zu vermerken

Dear Leander, 

In barter deals we are forced, because of VAT (Value Added Tax) laws,
to invoice you for the abovementioned accomplished services. We
invoice you in the barter for a fictive value of 1,000 SF
(Swiss-Franc), plus VAT. As a counter-move, send us a bill for the
same gross amount incl. VAT in SF. Each invoice should be equal to the
other by the dates of their payment. An exception will be made in
cases of publications from a foreign publisher: in this case, the
bills will be mutually written off. It is compulsary to invoice the
same gross amount including the relevant VAT record (1,076 SF) and to
note on the bill that it is "cashless barter" («bargeldloses
Gegengeschäft»).


I hope that helps. Although I didn't do much traditional "research"
here, it will be helpful to mention two online dictionaries:
Marketing Wörterbuch
<http://medialine.focus.de/PM1D/PM1DB/PM1DBK/pm1dbk.htm> (Marketing
Dictionary)
Eng <--> German Dictionary, University of Chemnitz <http://dict.tu-chemnitz.de/> 

Please contact me if you need any further clarification on this answer
before you tip/rate it.

Good luck in your business!

Super answer - thank you very much! One tiny, nit-picking point: 
you spelled "compulsory" wrong! By the way, I was much amused by your
quotation of the MultiTranse version

I thought I'd see how a program called MultiTranse would cope with
this translation. You can see by the following result that such
translation programs have a way to go before they can be counted on!

With the gegengeschaeft we are forced for value added tax-legal
reasons to place to you achievements specified above in calculation. 
The gegengeschaeft we place to you with a fictitious value of CHF
1'000.?  plus VAT in calculation.  In response you send us a
calculation in the height of the same gross amount inclusive VAT in
Swiss Franconia.  Each faktur is to be settled within its date of
payment.  Exception forms the gegengeschaeft with publications of
foreign publishing houses:  here the calculations are mutually written
off.  Compelling, is the same gross amount including the respective
VAT set to invoice (CHF 1'076.?)  to note and the calculation with
"gegengeschaeft by transfer"

Dear Leander, 

Thank you for the ratings, and apologies for the spelling mistake - my
spell checker somehow missed it!