Simple Fileserver: What to go with?

I'm looking to get a simple file server set up for a small office network (<20 users), and am looking at three options I'm hoping someone here with firsthand experience can give me some quick "Yeah, that's fine" or "You'd better read more into it" advice on.

Basically, the choices would be a cheap Linux-based file-only box (or maybe a NAS box), a Win2K3 server, or an XServe.

Our network is about 2/3 Macs, and my main goal is to have centralized file storage accessable to everyone in the office. The thing I'm most afraid of is permissions issues: I don't want to see user X saving a file while logged in as themselves, then user Y not being able to get to it without manually adjusting its permissions, and of course directory-level protection is also nice.

I understand how UNIX handles things fairly well, so I'm wondering if Apple has a clean way to smooth out these sorts of things in Panther Server. I've seen some significant annoyances along these lines using the Client version of 10.3, and am curious if there are tools in the server version to deal with them. Likewise, are there any particular issues with Windows clients?

I already know what to expect with a Win2K3 server--I've previously set up one in a mixed network, and although it was a MONSTEROUS pain to get working initially (an experience I hope never to repeat), it's run smoothly once setup was complete, outside of some file name issues on the Macs connected to it.

No idea where a Linux server and/or NAS fits into this spectrum.

For reference, I really want to go with the XServe if at all possible for a number of reasons (Netboot potential/home directories on server being at the top of the list), but I want to make sure it's not going to cheese anybody off if I go with one (particularly not PC users, since cross-platform ease is the way I've sold getting a server in the first place).

I know this is needy and I should be digging in Google, but help?

Thanks for the tips.

Having done some pricing, I'm already well aware that the XServe is (in terms of hardware cost, not counting my time) the most expensive option, and I'd have bet money that the XServe would be the easiest to initially set up, with Linux requiring the most tweaking to get running.

That PDF, which I handn't seen before, does cover a lot of what I'm interested in, but I'm still curious if people have seen annoying permissions issues or if its as smooth and easy as Apple makes it out to be. Guess the really annoying quirks with the Finder's permissions control has made me wary.

Ok, to experiment I've been messing around with SharePoints, a piece of shareware that lets you get at most of the more detailed user/group/shares features in the non-server version of OSX.

The good news is, it seems to work pretty well with both the Macs and Win boxes. The bad news is, it's giving me EXACTLY the problem I was afriad of, and would be enough to make me not go with an OSX server if there isn't a way around this in the full Server OS:

User A connects to the server, then copies a file to it. The file locally defaulted to that user as owner, and read-only permissions on the group, so that's what it has on the server. When user B then connects and tires to open the file, they've of course only got read access, causing hassle.

What I WANT is directory-level permissions, which I've set Windows Server up to do in the past--regardless of what permissions the file is saved with, anyone in the correct group can read and write files in the folder so long as they've been given access to the folder.

This prevents hassles like "Hey, Bob, you gotta change your file to R/W so I can edit it." That's fine for some workplaces, but an unacceptable pain in the rear where I work, where document-level security is an annoyance rather than a feature.

Surely OSX server can do this for me? Anybody who's used it this way?