The OS is a bit limited on laptops as yet. The dual cores run fairly well, but there are two major bottenecks according to WinSPR(Windows System Performance Rating). These are graphics cards and storage subsystems. I have some inside data, but am NDA'd on specifics since the specs are not finalized. Most high end graphics cards are scoring in the 3.5 to 4.2 range. This will allow Aero to run without problems, but presents a challenge for the future due to power constraints. Storage is a differing problem. The rating is, in part, based on storage capacity and 2.5" platter drives are not scoring above a 3. Since WinSPR bases system score on the lowest score, a 3 is the highest overall score I've seen.
If you are basing a purchase on eventually running Vista, plan on a dual core at least 2.0Ghz, at least 1GB of dual channel RAM(2 strongly preferred), high end graphics card with at least 256MB of dedicated RAM. Plan on upgrading the HDD as higher capacity drives become available. Hybrid drives are expected to score better, but I haven't heard any definitive answers on chipset support.
In relation to the comment on the Z60t, integrated graphics chipsets typically score a 2 and will not be able to run Aero.
I'd be tempted to wait for memron, since they will be available very soon. The Yonah dual cores score 5 in WinSPR and meet the highest current requirements. Either way you should be fine, but if getting Yonah a T2500 is as low as I'd go.