In reply to TryfAndy:
Depending on how bad it is, a week might not be enough. I would go and see a physio instead asap. I have had it last winter for a few months and what I was told by physio was: Ice the area at least once a day and do the following exercises. Tin of beans, hold elbow at 90 degrees and move wrist upwards (then release tin with the other hand), move wrist down again and repeat 10 times. That was when it was really painful.
The next exercise is to do the wrist curl up and down with the tin once you can tolerate it.
Also 10 times stretching, by holding arm outstretched and bending the wrist downwards.
Massage treatment of the physio really helped it,too. But I think Ibuprofen and a weeks' rest might be a bit optimistic if it really is tennis elbow! Good luck, let me know how you get on...!