In order to use Acctivate from a remote computer, you will need to use a remote connection tool in order to remotely connect and run Acctivate on the local network. Terminal Services is an option if you have a Windows 2000/2003/2008 Server.
You should consult with a Microsoft Certified Systems Engineer (MCSE) to assist with configuring Terminal Services.
Note: Windows Server 2003/2008 Standard Edition is usually packaged with standard CALs (client access licenses). Only two remote users will be able to connect using Terminal Services at a time and these users must be in the administrators users group. You must obtain TS CALs (terminal services client access licenses) to allow for non-administrators or more than two users to connect at a time. TS CALs are different than the standard CALs and none are typically included. Pricing information is available at microsoft.com.
Once Terminal Services is configured on a Server, you can then use Remote Desktop Connection utility to remotely connect to your terminal Server. See this article for more information on this.
Note: TS CALs cannot be added to a Windows Small Business Server 2003, so only two remote users will be able to connect at a time and they both must be in the administrators user group.