Pausing calculations for a fixed amount of time

Is there any way to pause R for a gvien time period, i.e. without the
need for user intervention? I've got a loop that I want to have work
as hard as it can as long as there is data coming in, but when there
is no new data, I would like it to pause before checking again.
Something like in the following construction:

Set up environment: load libraries, ?establish database connections, etc.
while (time_is_less_than_x) {
? ? Check for new data in database
? ? if (newdata) {
? ? ? ? Analyse data (lengthy calculation)
? ? } else {
? ? ? ? pause
? ? }
}

I'm working on Windows Server 2003, but if there is something that
only works on Linux, that's of interest too.

I am aware of the ask option in par, pause in the package sm, and
prompt.user in Zelig, but they all require user intervention to start
again.

Mikkel