PST is not like GST, in that you don't get credit for the PST you pay, you only remit what you charge to the provincial government. If you don't charge PST, then you don't remit anything to the government, and you really don't need to worry about it. You can still have a PST account set up and when you post bills, show both taxes you paid, and you can keep an accounting o fhow much PST you have paid, but other than being able to curse the government for how much tax you've had to pay, you really won't need to look at the account.
Now, if you do collect PST, there are some cases where you can claim back PST you have paid, if you can prove to them that you are not the "end user" of the purchase and that the person you sold it to has paid the PST. It's usually more work than it's worth though, unless it's a large amount, much easier to give your vendors a PST exemption certificate and just not pay it on items you are using for re-sale or manufacturing. Of course, in order to claim any back, you have to be registered for PST and remit reports to the government.
Hope that helps.