i have Sibelius G7, and i found the midi entry to be kind of flaky and
kooky, and the "Kontakt" playback to be kind of quirky too.

So I just stay with step entry.

There are some free DAW programs out there that have midi sequencing
and audio recording. See if you can play with one of them if you don't
have any DAW software. If you can get your rig working fine, then you
know Sibelius is what's letting you down.

If you can cough up $79 or so, I would recommend the M-audio Audiophile
24-96 card. The midi and drivers are great on it. And it has ASIO
drivers, which will give you a gateway into professional recording
applications. It also has GSIF drivers to drive Gigasampler. It also
works well with Windows Media Player type things. So it's basically a
great slug-around card.