Brass is a 32 bits software. Anyway you can use it without any problem with a 64 bits OS.
Nevertheless special attention should be taken when usins as a VST on a 64 bits host (Cubase for example).
The best advise i can give you is that Cubase allows you install two cubases on you computer, one 32bits and one 64bits...
When you plan to use a 32bits synth in one of your projects, then use your 32bits Cubase.
Our synths next updates will be developed for 64bits environment...Nevertheless we have no release date announced at that time.