Welcome to the forums TLG and congrats on your new toys. I'm sure you will enjoy the K-x it is a fine little camera, and it's low light capabilities are amazing!
One note of caution; on some old lenses there is a pin, called the "ricoh pin" which was used to transmit information from the lens to Ricoh bodies which also used the Pentax lens mount. The problem is that lenseswith this pin can get stuck on Pentax DSLR bodies like your soon come K-x. Not to fear however, the pin is easily recogniseable and removeable. Many different places on the web show you how, like this one
here. I don't know if your new-to-you Vivitar has the dreaded pin, but it doesn't hurt to check and it's very simple to remove.
NaCl(enjoy your new K-x and we're waiting with bated breath to see some pics)H2O
well maybe not bated breath, but pics will still be appreciated.