You can download Sequencer Plus for free from
http://www.voyetra.com/site/kb_ftp/340ftp.asp It's a DOS program; (it might work if you 'boot to command prompt' when starting a Windows XP box, if that's what you have. You'll also need to download the appropriate driver pack for whatever MIDI interface card you can scrounge (same page, also free). Luckily, it seems Voyetra supported various Creative cards -- it's hard to find an MPU-401 these days!
Frankly, the safest way to get your songs back is
- find an older machine in somebody's basement
- Put DOS on it
- find an old soundblaster card
- install the soundblaster and drivers (free from Voyetra Turtle/Beach)
- install seqplus gold ...
That way, you don't risk your current PC by trying to install / run antique software/hardware in it.
Unfortunately, I don't have a machine set up to run SeqPlus (I haven't used it in at least 15 years ....)
Good luck,
-Jim