PC can access TC .. just load airport utilities on to the laptops.. that makes it easier to locate the TC.
Set the disk sharing area, workgroup correctly.. usually WORKGROUP..
Turn on the guest account.. read and write access also makes life easier.
Also windows can have a hard time with typical TC name.. like fred's time capsule.. that is illegal name in SMB.. change to simple short name.. no spaces pure alphanumeric.. same with wireless names (SSID to normal humanity).
Note the second question.. should you??
Mixing data and TM backups is not wise in the long run.. TM will mess up if it cannot access the disk.
Read Q3 here. http://pondini.org/TM/Time_Capsule.html
Also go back to top menu and read the FAQ.. TM is much more complex than you think and TC is primarily a TM target .. anything else you do.. remember one day the TC will die. it has no way to back itself up. and all your files will go with it..
I repair them and I am sitting here tonight with a dead 1TB .. had lots of data poor lady off loaded from her laptop.. and now it is all gone.