Timmy,
Sibelius 5 works directly with the Vienna Instruments and you don't need to worry about Kontakt 2. SIB5 can host VSTs.
So yes assuming your computer specs are up to it you should be able to make good music with SIB5 and VSL SE.
Things are getting even better with the new software the Vienna Ensemble - except that it's only in the beta stage and there are problems with getting it to work with Sib5 which I haven't yet resolved.
PS yer what DG said but without the reference to female underware.