You can get the current time in HH:MM:SS format by using the below syntax in FormCalc.
$host.messageBox(Num2Time(Time(), "HH:MM:SS"));
For different formats please check the help in your designer.
I am not sure about getting the user name from the local computer. I am under the impression that it is not allowed to read the local user specific information for security reasons but I could be wrong.
Thanks
Srini