I have two HP Notebooks with more or less identical spec to your Sony Vaio right down to the Intel 740cpu (upgradeable to an Intel 760(2.0GHz), 770 (2.13gGHz) or 780(2.26GHz).
I've gone to a full 2Gb of Ram in both and a 320gb WD HDD in one of them
Both currently run XP-pro sp3
If both Memory slots aren't accessable through an access cover in the bottom some manufacturers "hide them"
under the keyboard (HP and Some Dells) or a removable section of the palm rest (Compaq)
If your notebook requires DDR2 PC2-4200 it will certainly work with not only PC2-4200 but it will happily
run on PC2-5300, which is usually easier to find and cheaper (used) on ebay.
but if you are willing to buy NEW memory Newegg sells GSkill 1gb DDR2 PC@-4200 laptop sticks for $16.99 each.
NEW memory from Newegg will of course have a warantee that used memory off ebay won't
As for the Hard Drive? your Intel GM915 Chipset will work with ANY IDE, PATA, ATA-6 HDD.
the prices on IDE drives are typically 50%-100% more than similarly sized SATANotebook hard drives.
WD still makes their 320gb PATA/IDE notebook drive, Newegg Sells them for $89
But they also sell 250gb and 160gb drives