seavixen32 has given you the perfect link for the 1315 printer :-) I myself have the identical printer, and I also needed the 64-bit version of the
driver to install it on Windows 7. There was no problem installing it - everything went smoothly, and the printer prints fine :-)
About the 855C: I did some searching, and it seems that this printer model is so old that there are no
drivers for it under Vista or Windows 7 :-/
However, maybe someone can give you more information over here in the HP Support Forums:
http://h30434.www3.hp.com/t5/Printer.../bd-p/Software
I got some good help there when I was having an issue with an HP device.
I also found
this, where it is suggested to use another printer
driver for Vista to make the 855C printer work, but I'd want to make sure that this is possible for 64-bit Windows 7 before experimenting around... :-)