Simple,
1) Make sure your computer at home and at your office belong to the same subnet. Example office pc (192.168.0.10), home pc (192.168.0.11).
2) Install IIS on your source computer. You can check for this under control panel, add/remove programs, add/remove windows components.
3) Enable Web Sharing on target folder. Right click on folder to be shared. Go to web sharing tab. Click on Share this folder. Check Read, Write and Directory Browsing. You have now shared this folder.
4)From Web Sharing Tab, go to Security Tab, see if Everyone is enabled (if you want more security enable access for IUSR_computername)
5) From home pc, you can view this shared folder by launching Internet Explorer and going to the url of office pc. Ex: http://192.168.0.10/mysharedfolder
6) You can now download your files.
Another version of this is via ftp. From ISM (Internet Services Manager) located inside Control Panel/ administrative tools, you can enable an FTP server. The root folder for your ftp is a shared folder located in that computer. You can then use an ftp client (cuteftp or ws_ftp) to download and upload files to and from office pc.
hope this helps.