Exactly as Squidge wrote
in last Olly press ALT+F1 (Plugins->Command Line->Command Line)
in editbox type
bp CreateFileA, STRING [[ESP+4]]=="yourfilename"
press F9, when Olly breaks press CTRL+F9 (run until return), press F8 (one step) and read value at eax - it's handle for your file
so in Command Line plugin add new breakpoint
bp WriteFile, [[ESP+4]]==90
(of course you must replace value 90 by your eax value)
and go for debugging
hope this helps