You need one of the XA1541 adapters available via a certain auction site. These connect to the printer port on the PC and allow you to send files to a 1541 disk drive. There is also n XE1541 adapter but I am led to understand that the XA1541 is better.
That is the type of adapter I was thinking of, however, I would advise that you talk to someone like Overdoc over at Lemon 64 forums, to make sure that you get the right one; some of them aren't compatible with more modern motherboards but I don't know which ones.
Personally I would recommend the Catweasel PCI controller card for the PC. This PCI card allows you to connect original C64 drives, as well as standard 3.5" and 5.25" drives, to a PC and read and write to C64, Amiga, ST, Arch and many other file formats.
It is quite expensive at £74.99, but it is strongly supported, with the developers releasing firmware updates regularly to add new features to the card and fix any bugs users report.
A member of classicamiga called Demon Cleaner owns one of these Catweasel controllers, so if you need to ask some questions before you look into buying one then I recommend you have a chat with him as he should be able to answer your questions. He is a C64 user so has used it to read and write C64 disk formats.