First thing I would do is have the machine checked out at the local sew & vac. It's been sitting for 15 years and no telling how well lubricated it is or what shape it's in.

I did a google search for a Singer 5817. Allbrands has it for less than $20 with a Google rebate going for first time buyers.

One thing I figured out is that this machine threads like most Singer machines do. If you are completely new to sewing, yes you will be completely lost. If you have had other machines, you shouldn't have any problem threading it.