VideoServer is a plugin for MSPro 6.x that allows you to link the MSPro timeline to external encoders (TMPGEnc, CCE, ManConcept MPEG, WME etc. etc.).
This process is called "frameserving" and is accomplished by starting the VideoServer plugin in MSPro. It then creates a short pseudo *.avi on the HDD which you load into the external encoder. Once the encoder is set up and started MSPro will feed the encoder the timeline for processing. VERY cool.