Hi amie
got to that line in your BSP from which you want to start the debugging. Set here an <b>external</b>breakpoint. thats all. Now you call your BSP in the browser.
And in the SE80 under Utilities->Settings->AbapEditor mark external Debugging.
Take a look.
http://help.sap.com/saphelp_erp2004/helpdata/en/17/00ab3b72d5df3be10000000a11402f/frameset.htm
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