This link should land you on the membership page:
http://www.spintops.org/membership.htmlFrom there you have two options.
If you want to pay with Paypal, click on the orange button that says Join ITSA. Actually, if you are renewing, you could just send your $10 Paypal payment to "treasurer_AT_spintops.org"
If you want to pay by check, click on Download Membership Form, and send it together with your payment to the address listed.
This photo shows some (but not all) of the envelopes I mailed today to 5 countries with the new embroidered patches to members who renewed:
PS: I need to change the toner on my laser printer, so the letter that accompanies the patches doesn't look very good. Sorry.