You can determine the plugin ID of any VST by opening a staff in Notion with that VST plugin assigned to it, then press "Shift-I". The first four characters in the parentheses listed after the VST name is the unique VST ID. In Notion 4, you can just use this four character identifier as your Plugin ID in your plugin rules, but I'm not sure if you can do that in Notion 3, I never tried.
If that four-character doesn't work as the Plugin ID, you can convert it to the numeric equivalent. I don't have SampleTank readily available to open in Notion (I only use 64-bit Notion and haven't jBridged it yet), so I can't figure that one out directly for you. But let's use another one as an example you can follow to find it yourself.
I'll use Miroslav Philharmonik as an example. The VST ID for PC is revealed by Shift-I to be "PH10". First we have to convert each character to its ASCII equivalent, but in hexadecimal: 50-48-31-30. You can look up ASCII codes in hexadecimal here:
http://www.ascii.cl/htmlcodes.htmThen, we treat those four HEX codes as one large 8-character HEX code, and convert to a decimal number (which is the Plugin ID that Notion needs in the custom rules file). I just used a programming calculator, entered 50483130 as an 8-diugit hex number, and told it to convert to decimal. The result was 1346908464. I know that is correct, because that is what Notion themselves used for Miroslav as the Plugin ID in their ruleset.
So, if you follow this procedure for your SampleTank plugin, you should be able to derive the numeric Plugin ID. Or, just let me know four character ID comes up using Shift-I and I can do the conversion.