ANSWER:

I found a forum post (now deleted) which describes a solution for Windows Home Server. There is also another post that covers Running Dropbox as a service on Windows Server 2008. The description below is for WHS.

First, run the Dropbox installer using the command line switch /D=C:Program FilesDropbox (with no quotes) to install Dropbox into the Program Files directory for all users.

Then here an updated version of the procedure given on this link:

Since Dropbox will normally only work
when a user is logged in, we will have
to install and use it first via remote
desktop, before it can be turned it
into a Service.

1. Remote desktop to your WHS as administrator
2. Get DropBox from their website.
3. Install and configure Dropbox as you like. e.g. I made a special share on my WHS named Dropbox before the installation and linked Dropbox to this share. Then exit dropbox from the system tray.
4. Similar to Foldershare, you will need instsrv.exe and srvany.exe from the Windows Server 2003 Resource Kit Tools.
5. Copy instsrv.exe to C:Program FilesDropbox
6. Copy srvany.exe to C:Program FilesDropbox
7. execute "C:Program FilesDropboxinstsrv.exe" Dropbox "C:Program FilesDropboxsrvany.exe"
8. execute reg ADD HKLMSYSTEMCurrentControlSetServicesDropboxParameters /v Application /d "C:Program FilesDropboxDropbox.exe"
9. execute reg ADD HKLMSYSTEMCurrentControlSetServicesDropboxParameters /v AppDirectory /d "C:Program FilesDropbox"
10. Delete or move the shorcut to Dropbox away from the startfolder (Start -> All Programs -> Startup) on the startmenu.
11. Move (cut/paste) ALL the files from C:Documents and SettingsAdministratorApplication DataDropBox to C:Documents and SettingsDefault UserApplication DataDropbox
12. execute net start Dropbox

by Gnoupi from http://superuser.com/questions/42012