I have a vaio srx87p which isn't a picturebook but is the next smallest size up, under three pounds. I know for mine that the memory was a bit harder to swap out then the hard drive. The hard drive on mine has an access panel but the memory I had to remove the whole back side of the vaio. You shouldn't have a problem with either as long as you have the correct size screw drivers. SRX87 comes with 256MB of ram which I believe the picturebook also does. 128MB of it is onboard, not removable. The other 128mb is removable, and is what you'll need to remove to be able to place a new 256MB simm into the only socket there is. Swapping out 128MB for a 256MB will give you 384MB. Do you really need 384MB for recording? Not really. If you setup your laptop correctly for audio recording you'll find out that you will only be using less then 200MB of RAM. With all the needless services disabled and disk caching disabled you'll be writing directly to the hard drive, which is what I'll talk about next.
Personally I wouldn't do any recording with a laptop unless you have a fast hard drive. I believe your picture book, along with my srx87, came with a slow 42000RPM hard drive. Technically, this is too slow to write audio that is 48K@24, and you'll find there is nothing you can do to prevent dropouts because the hard drive is simply to slow. I suggest buying a 72000rpm hard drive, that way it is fast enough to write higher sample rates with out falling behind and producing drop outs. I believe any 9mm hard drive would work but check your specs for the picturebook off of Sony's support page.
So get the hard drive first then worry about the RAM.