Well, it always depends.
I run servers for others and I can't see any "real" advantage of running a server for your email and website local to you. The line is too expensive, that's just the main concern. I would rather find a local datacenter and colocate the server there. Operating system on a web and mailserver, I would suggest FreeBSD (which we run for HTMLCenter, btw). Ports work really nice. Apache (web), vsftpd (FTP server) and Postfix are setup really easily.
Hardware-wise, a Celeron, 256 MB RAM and maybe a small RAID system will work. You can skip the RAID too, but I am thinking email is somewhat critical.
If you need a HOWTO for a webserver setup, check this out, I recently added a HOWTO for FreeBSD setup:
http://www.ladse.de/index.php/Documentation
Regarding your fileserver, you don't really need much here to get started. I would suggest buying a Celeron, 512 MB RAM and a RAID system (RAID 1 maybe, or RAID 1+5) for basic security of the files hosted.
Raid 1 does the mirroring, while Raid 5 has an extra parity HDD. For Raid 1 you need minum of 2 harddrives. So for example, 2x 160 GB hdd gives you 160 GB to use, the other 160 GB are kept as a mirror. As for Raid 5, you need a minimum of three HDD. Two can be used for data and the third is used in case one of the two being used breaks. So you can recover data.
Raid 5 takes longer to recover - in general. But Raids are like science. I'd suggest a read on tomshardware.com to find out about Raid controllers.
For the operating system you will just need a basic BSD or Linux install, I would suggest FreeBSD again, or if you want Linux, Debian, to you. Debian is quite stable and has a big community of supporters.
Redhat and SuSE are not my choice, they are rather bad examples for what you can do to Linux. Other BSDs are OpenBSD, NetBSD and DragonFlyBSD.
When you have FreeBSD or Debian running, you would need to install Samba. Which works really well with your Windows PC (client-side). Through Samba you will be able to create shares for your users where they can save their files. As for remote access, I would suggest to setup a small VPN (the fileserver can handle that as well), to have your road warriors become part of the network and then they can access their shares (Samba) just fine, without any bigger security issues and so on.
By the way, I am available for contract work.
hehehehe...
Hope this helps,
Till