Use iMac as monitor/Low Latency HD Video "Capture (transmit)"

I recently inherited a 2007 iMac 24" with ATI 2600HD Pro GPU. I understand the only way you can use an iMac as a monitor is to have a late 2009 model.

However, I'm wondering if there is an external box I could use to use it as a monitor. I have a PC workstation that is a powerhouse and I'd like to use both. However, I don't want to have two independent large monitors on my desk if I'm only able to use 1 or the other.

Ideally, I'd like to use the iMac as a monitor for the PC but would also like to have the ability to switch it to the iMac display itself (like a KVM).

Is there a hardware solution that would allow this? Perhaps a firewire graphics interface that would allow my iMac to function as a monitor (because the Mini-DVI not Mini-DisplayPort is not an input at least that's my understanding).

Perhaps I have some misinformation or if there is a hardware solution I'd like to hear it.

Thanks,
JOe K.