I downloaded the IAT word script from the inquisit page and would like to know, if its ok if i have in two of the four categories only one stimuli per category
Sorry, I don't understand what you mean here. The code you posted has the exact same number of stims as any other standard IAT / as in the original template.
But what is the group number for?
The group number is a new feature in Inquisit 4, currently in beta. The publically available IAT scripts are for Inquisit 3 and thus don't make any use of group number. You can ignore it for now and just leave it alone at its default value.
Last question: That the blocks are presented in a randomised order is programmed automatically right? I don't need to program this additionally?
The order of blocks is counterbalanced between subjects according to the supplied subject number (odd vs. even). See the script's <variables> element for details.
I generally recommend you work through the various tutorials included in the Inquisit documentation before moving on.
Regards,
~Dave