i wouldn´t work on acid or whatever for medium sized productions.
two professional sequencer programs are available: cubase sx 3 and logic audio. however, emagic logic audio runs on mac (only older versions on pc). therefore, i would recommend cubase sx 3.. even if i hate it and would like to throw the computer out of the window at times. when something does not seem to work. you can do a lot with cubase, supports vst instruments, load your battery sampler or software synth in cubase, you can record audio and midi, cut, paste, edit, print the score, eq, effects, ... then you need a good soundcard, for multitracks i´d recommend the company RME, no you won´t get that for free (unlike some of the others, you just need to look for them).. i did some small demos or remixes mixing the whole thing in cubase, it aint high rollers stuff, but you didn´t say you wanted a multi million $ studio (with protools and focusrite and the big t.c.´s and neumanns) so..