Yes it all you have to do is register to get it.
However, since you are posting in the WHS avast 4 Windows Home Server forum are you using that avast product ?
The reason I ask is that you shouldn't need anything other that what came with the 'avast! Professional Family Pack.
avast! WHS license information
The license for avast! WHS is in the style of a license file. You will be sent this, via email, upon making a purchase. You will then need to save the file to your WHS server, ready to be loaded into avast! Once saved, you should open the avast! WHS console, select the licensing option and choose insert license file. You can then browse the file system within the WHS server, for where you saved the file, select the file, and click OK. The file will then be loaded into avast!
Should you have purchased the 'avast! Professional Family Pack', then this includes avast! professional licenses for upto 10 machines (in your household). The license information for this is included within the license file and can be deployed to each machine by selecting the Deploy avast! professional edition license to all computers button.