the ready boost of vista is to allow users with machine using older processor (P4 for this matter) that has an extended memory card slot, so it can act as a n additional memory. and windows can avoid system degradation by reading too much in the disk using its virtual memory page. we know for a fact that disk I/O can hog 100% of your CPU resources.
but if your machine is already configured to its maximum memory, i don't even think that is going to be of a great benefit, specially when you are using Linux.
I consider P4 to be an old processor if you are using Vista, since Vista's entry level machine is actually the dual core; core 2 duo with atleast 1GB of RAM and atleast 128mb of VRAM.
Vista by itself is really a resource hungry OS since it has improved so much in its graphical features, nearly or almost ripping-off the MAC OS 10. this is why, the MAC OS, when they used the intel processor, thay have made sure that it is already using a dual core processor.
if you add the M$ office 2007, which is another resource hungry application, then your machine starts to feel the load and somehow would cease running and start walking, and eventually crawl.
if you plan to use Vista in your P4 machine even configured to its maximum capacity, in one or the other, you may feel disappointed because you will not get the performance you are expecting. (i tried vista in a P4 3.4GHz, HT with 2GB RAM, 128mbVRAM, 80GB hd, with SD card, and my machine was just walking under the moon. LoL)
With Vista out, and you think of retaining your current machine (w/c is not dual core) then, Linux is the best alternative for you, unless you want to stick it out with XP.