have you checked to make sure your motherboard supports 128MB modules? some older motherboards are limited to 64MB ram modules.
IWill XP-333 / 384MB PC2100 DDR / AMD T-Bird 1.33GHz (o/c to 1.40 until I get a better CPU cooler!) / VisionTek GeForce4 MX440 / SB Live! X-Gamer 5.1 / Maxtor 20GB 7200 RPM HD / Toshiba 8X DVD / Sanyo 40/12/40X CD-RW / Win XP Home