I started with software I wrote in vax vms basic and fortran for generating tone rows and inversions and deriving the chord multiplication matrix espoused by Pierre Boulez
Then I wrote some similar programs in vic basic for the commodore vic20
next came pro 16 for the commodore 64
closely followed by pro 24 for the atari st512 and mega2st
then e-magic logic for the atari as well
later came e-mafic logic (the daw) for pc and cubase vst32 score V2
then cubase vst32 score v5.1 for pc
also finale notepad+ 2k2, 2k5 and 2k7
currently using cubase v5.5.3 for pc,
reason 6.5 in xp, reason 8 in win 7, reaper and fl10producer (rarely use this but it is installed for collabs) also have supercollider and puredata (a open source version of max) installed for experimental work, and tuxguitar tabbing parts for clueless guitarists
have garritan gpo 3 and 4, JaBB 2 and 3, CaMB 1 and 2, miroslav philharmonick, komplete 8 ultimate (moving to 10 next year along with a komplete kontroller)
for beginners I recommend reaper (free never ending demo that works, $60 to license) and suggest that you look at kvr audio free plugins/libraries