According to the specs on those pages, both notebooks will have Core 2 Duo processors clocked at up to 2.4GHz, Intel GM/PM965 chipsets, 802.11n Wi-Fi, either Intel GMA X3100 integrated graphics or a discrete NVIDIA Quadro NVS 140M graphics chip, and wide-screen 14" displays with a resolution of either 1280x800 or 1440x900. The R51 will be 1.2" thin and weigh as little as 5.2lbs, while the T61 will be as thin as 1.09" and as light as 5lbs.
Bundled operating system choices will include Windows Vista x86 and Windows Vista x64, and Lenovo will apparently offer Windows XP Professional as an operating system option for the T61. Both notebooks are scheduled to ship in May, although some variants (including the ones with discrete Nvidia graphics) won't become available until July. (Thanks to DailyTech for the tip.)