see: http://support.microsoft.com/kb/260910
Updates and fixes to Microsoft Windows 2000 are distributed in service packs.
Support for Windows 2000 ends on July 13, 2010
As you can see, your system appears to be a little outdated, perhaps look at a new computer.
System requirements for 3.5 .NET Framework :
Supported Operating Systems: Windows Server 2003, Windows Server 2008, Windows Vista, Windows XP
http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=22
So if your mother's job requires .NET Framework, then she'll need to upgrade her computer.
The above are things to consider.