Is there an easy way to set up E-Mail notification when a Windows 2008 server's hard disk is getting full?
From Vista/2008 onwards Microsoft added the ability to attach actions to events, You can setup a e-mail alert to be sent whenever the event id 2013 (disk drive near capacity) is triggered.
Open the Task Scheduler MMC, start the Create a Basic Task Wizard, give it a name and select on the event trigger. Set the Log to "System" Source to "Srv" and Event ID to "2013".
Then assuming you have a usable SMTP server just set the action to send you an e-mail.
The information you get is pretty basic, there are a lot of good monitoring tools freely available that handle this as well (SpiceWorks is one I recall).
This is simple to accomplish with Powershell. This is an example.
If you don't have a local SMTP server you can download this little tool and follow the same event scheduler instructions, except you make a batch file containing this:
sendemail.exe -f YOU@gmail.com -t YOU@gmail.com -u "LOW DISK SPACE ON COMPUTER!" -m "LOW DISK SPACE ON SERVICES!" -s smtp.gmail.com:587 -xu YOU@gmail.com -xp YOURPASSWORD
Make sure you include the path to sendemail.exe at the start of the line if you don't put them in the same folder.
The sendmail.exe tool is pretty useful if you don't want to use a local SMTP or want to scripts to send emails.