Library LookUp redux - success!
Unfortunately, performance isn't so great. With IE6, it takes about 10-15 seconds, while with Mozilla, it seems to take even longer. But I think this is an artifact of Vistaweb (the NLB catalogue) - it takes quite a long time even when searching directly from the site.
Here is the link (click and drag to your Links toolbar (in IE) or Personal toolbar (in Mozilla) and pretend that you trust me, then when you're on any page with an ISBN in the URL just click on the button (called NLB Library Look-up - but you can rename it) and it will look it up in NLB. Note that it will just open in the same window.
NLB Library Look-Up