I have a suspicion your problem is Vista. But not because Vista in and of itself is incapable of running on your hardware.
Let me explain:
I've used Vista for around a year on a 2.2GHz laptop. For me, it runs absolutely perfectly (or as perfectly as any Windows OS can, but that's another discussion

). However I switch off around half a dozen services after installing, I also tweak the pagefile and a number of other settings to improve performance.
I've noticed that on some machines (mostly laptops) when I've directed others who are suffering from horrible Vista performance problems to do these same things that it makes no difference. They still get horrid performance.
This surprises me because I'm really impatient and unforgiving with how responsive a system is and I have Vista running effectively as quick as XP, yet others who will generally put up with the crap XP throws at them suddenly struggle with what are appearing at my end to be minor performance differences.
My conclusion: Vista just runs crap on some machines. There's no way to get round this unfortunately.
What you could try is this:
1) Have you reinstalled Vista since you bought the laptop? This should be the first thing ANYONE does with a new pre-made machine from somewhere like Acer, Dell, HP, etc, etc. It gets rid of all the additional crud the company puts on the machine and allows you to cleanly install the newest drivers.
So, head to the acer site, grab the latest drivers and try a clean install.
The services I suggest killing are:
- Windows Search (even if you search for things regularly, it eats LOADS of CPU power, usually right in the middle of you doing something important. MS seem to have it on "normal" priority instead of "lowest" and with no checking if you're doing things -- This has improved under Windows 7 I note)
- Superfetch (it's
supposed to pre-load DLLs and often used programs into RAM. In reality it just eats CPU power and adds little in my experience, switching it off won't make performance any worse than XP)
- ReadyBoost (this is optional, but it's likely you'll never make use of it if you have 4GB of RAM)
Additionally set the pagefile to a fixed size of 4GB helps. This stops Windows constantly resizing it, holding it on a single section of the disk (and hopefully all in one section), you do this through
Control Panel -> "show all items" -> System Properties -> Advanced tab -> Performance Settings -> Advanced tab -> Virtual Memory Change button -> Untick "Automatically manage paging file size" -> Set "custom size", put 4096 in both "initial size" and "maximum size", hit "set" then "ok" on all the windows.You could try all that before a reinstall. You can set any of it back if you don't like the effects of losing Windows Search (personally I don't miss it.

)
2) Try XP on the laptop.

Hope there's something in there that helps.