Grid middleware is enabling resource sharing between computing centres across the world and sites with existing clusters are eager to connect to the Grid using middleware such as that developed by the LHC Computing Grid (LCG) project. However; the hardware requirementsfor access to the Grid remain high: a standard LCG Grid gateway requiresfour separate servers. Wepropose the use of Virtual Machine (VM) technology to run multiple OS instances, allowing a full Grid gateway to be hosted on a single computer. This would significantly reduce the hardware, installation and management commitments required of a site that wants to connect to the Grid. In this paper, we outline the architecture of a single-computer Grid gateway. We evaluate implementations of this architecture using two popular open-source VMs: Xen and User-Mode Linux (UML). Our results show that Xen outperforms UML for installation tasks and standard gateway operations. Configuration is similar to that of sites running multi-computer gateways, making it easy to keep site installation profiles Synchronised. Our VM gateway architecture provides a low-cost entrypath to the Grid and will be of interest to many institutions wishing to connect their existing facilities.