Is there a device that will let me run two computers on one monitor???

TIA

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Current System:
ASUS P3V4X
256MB PC-133
PIII 700E
Geforce SDR 32MB AGP
SBLive Value
PlexWriter 12/10/32A
30.7GB IBM Deskstar 75
DXR3 + 6x DVD-ROM
CTX VL950ST 19" Monitor