Tell me a reason why you want 64-bit. Do you even know what it's going to give you?
The ONLY thing 64-bit is going to change is the amount of addressable memory. In other words, instead of only being able to have up to 4 gb of ram, you can have 4 billion times that amount of ram. 32-bit means 2 to the 32 power. 64-bit means 2 to the 64 power.
That's great, but in order to use that extra memory, you gotta have programs that support it. I know for sure that I'll be just fine with my XPS 2 for a long time. Although it can only support up to 2 gb of ram supposedly, I doubt I'll be needing more than 2gb of RAM to do what I need to do for years. (A side note on that: why is the 915pm chipset limited to 2gb? Is it only because they don't make RAM chips that hold more than 1gb each?)
In addition, since the latest 915pm chipset, and at best the 915p chipset in a sager, can hold up to 2-4 gb of ram, you'll be waiting a long time for memory technology to provide you with enough memory to actually use 64-bit's advantage since notebooks can't just add more slots or use bigger memory chips due to size restrictions. One more thing-- pentium M 64-bit cpu's are a long way off. Check out anandtech for more info. They basically said that 64-bit pentium M's are too large to put in a notebook, and it's going to be a long time before they get small enough.
Bottom line: if you know for sure that you cannot live with 2gb or 4gb of RAM, then you need to wait a few years and buy a desktop that fulfills your needs (laptops will be behind desktops, so you'll wait even longer for them.)