There are, no doubt, better qualified people who can answer these questions however I figured I'd provide you with a relative newbies (me being the newbies) opinion.
From what I understand, the creation of the PDF isn't the greatest difficulty. Adobe provides a free service through its website (although I think you can only create a few PDF's that way) IIRC, there are even free Print to PDF programs out there.
However, creating it is only half the problem. Once created, the only way you can edit it is by using Adobe Acrobat (the full version, not the free Reader). Since the conversion to PDF doesn't necessarily always take into account precise settings of Word documents (AFAIK), this facility is greatly needed in order to make your PDF's conform to your desired look and preferences.
Programs like InDesign and QuarkXpress have the in-built ability to 'Print to PDF' and these programs are designed (or, more accurately, the reverse) so that their settings are kept and the resulting PDF needs little or no editing in Acrobat.
My recommendation to you is therefore that you consider what exactly you wish to accomplish with your work. Do you wish it to be of a professional level or do you just want to share your work with others through the PDF format? In the case of the latter, I'd just use the free PDF options and not really worry about whatever niggling inconsistancies crop up on the resulting PDF. In the case of the former... well... a professional uses professional tools, so fork over the cash for the tools
As for linking the file... well, it's like any file. You'll need webspace somewhere and you just upload it and use a link. If it's free, I'm not sure how RPGNow works with that (although I think you have to be a vendor to have the option of giving freebies whilst using their servers), but I'm guessing you'll have to just get some Geocities/Angelfire space and just link it like you would any other file for download.
