As explained on the FAQ, you have 6 activations per order.
If one PC doesn't have Internet connection, you can buy on one PC, take the .REG key to the other, then install the Trial: it will ask you to activate and, if there's no internet connection available, after a while it will present a menu with options, select "Activate Using a different computer with Web access" it will generate a code relavant for the NON-internet connected PC that can be used by going to this site with another internet-connected PC. With the PC with an internet connection, go to this web site:
http://activate.esellerate.netInsert the code you got from the other PC, than save the code the website will give back, return to the non-internet-connected PC, reply Yes to the Activation request, after a while the same menu will appear, select "I already have an activation key and would like to activate now", it should activate your product.
Of course, running FS9 and FSX on two separate machines, will probably consume more activations.