Surely it depends on what you intend to use the laptop for and whether or not you can do the same things on your PDA.
You should write a list of all the things that you want to be able to do with your computer equipment, ignoring whether either can actually do them. Write a big long list and then draw up two columns, PDA and Laptop and then put ticks next to each thing that they can do. You might find that some of the things you ideally would like to do with a piece of computer equipment, neither can do.
You should also write a pro and con list for each piece of equipment.
Total up both lists and that should hopefully give you a good basis for comparison.
If it were me and I could afford it, I'd buy both, but then I've already got two laptops (pc and mac), a PDA (z5500) and a desktop (pc) and numerous other gadgets! No wonder I'm poor!!