I think I want to use a timer?

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C#

C#4.0

The joys of not working with a design doc... This is the same application I've been working on for a bit of time as a side project (no "due date") and I'm now getting a bit further into it and hitting a bit of a snag.
This is the basic functionality of the app: I need it to log into a mail server, see how many messages are there, get some data from those messages and update a database. I've managed to get all that working and now for the problem, I need this to run every so many minuets (I'm thinking 5?). I've tried using a timer and I keep getting cross thread errors on my background workers (used to update the form). I'd post the code, but I kinda deleted it and well don't really have it any more. However all that I need is for the following to be called ever 5 or so min

cleanUpFiles();
bgwRetreive.RunWorkerAsync();

cleanUpFiles writes the status to a text box, and there are a bunch of writes using the progress updates in bgwRetreive. The only other thing I can think of right now is to have a loop running on a thread checking for a time stamp, and then running the code when it hits it? Though I'm not really sure how that will affect resources as I'd have to run it in an infinite loop waiting for a cancel of some sort?
Obviously this is the first time I've tried to do something like this, thus the problems.
Thanks in advance.