The Core2duo processor on the Acer is a much better processor. A pity it only has 1gb ram as Vista really needs minimum of 2gb to run well.
The Acer will only have two slots so to update you would need to buy 2 memory sticks at about £10 each. It is ikely the memory needed is :
2X 1GB DDR2 SO-DIMM PC2-5300 (667), 200 Pin, Non-ECC Unbuffered. But check with Crucial .
As the battery is now old and costly to replace you might be advised to keep looking or consider something new.