2GB Memory RAM Upgrade for the Lenovo Thinkpad R61 Series, T60 Series, T61 Series, X60 Series and X61 Series Laptops (DDR2-667, PC2-5300, SODIMM) at Amazon.com
2GB Memory RAM Upgrade for the Lenovo Thinkpad R61 Series T60 Series T61 Series X60 Series and X61 Series Laptops (DDR2-667 PC2-5300 SODIMM) - Walmart.com
Steve Greene's Blog by sgreene570
Upgrading the CPU in ThinkPad X61 — Wenting's Web Page
CMS 8GB (2X4GB) DDR2 6400 800MHZ Non ECC SODIMM Memory Ram Upgrade Compatible with IBM Lenovo® Thinkpad X61 Notebook Ddr2 Pc6400 Sodimm - A41 at Amazon.com
X61 upgrade & Middleton BIOS - Thinkpads Forum
4GB 2X2GB Memory RAM for Lenovo ThinkPad X Series X61 (7674ES7) 200pin 667MHz PC2-5300 DDR2 SO-DIMM Black Diamond Memory Module Upgrade System Specific Memory - Newegg.com