Your description doesn't say anything about getting the most recent drivers and installing them, nor does it say anything about making sure the COM port that was assigned when you installed drivers matched what BCtool is expecting. You might have to dig through Gigaware's (or RS) website to see if you can find up to date XP drivers, or perhaps find the ASIC website. Every one is kinda different that way.
You can see whether you have a COM port assignment in Device Manager. Perhaps XP recognized it and installed, even if the drivers aren't totally up to date. I'm not at my PC at home, and am restricted on this PC as to what I can see here, but if memory serves me, it would be Control Panel/System/Hardware/Device Manager. If you have an assignment, make sure the port is actually available (some Blackberrys and other devices load a driver, and it remains resident - meaning it ties up a port - whether the device is really connected or not, for example).
The author of BCtool, along with numerous users, are available on this Yahoo group;
bctool : bcTool
73 Mike