A lot of factors involved. How will you be using your computer? I know you said IM but that is pretty broad.
If you will be doing lots of video editing you probably want a decent dedicated video card.
If you will be running lots of automated programs than you probably a quad core.
Also, if you do not absolutely need a laptop I'd recommend getting a desktop.
If something goes wrong with your laptop, have fun getting that thing open, then tracking down the parts to fix it. Especially if you motherboard goes, that is gonna be a bitch. Also upgrading parts on a laptop is not fun at all, even an hdd can prove to be an ordeal, never mind memory, cpu, video card etc.
Now if something goes wrong with your desktop you yank off the side panel, rip out the old part and put the new part in. You will be able to replace all parts and upgrade all parts easily, so you will be able to grow with your PC.
If you build your own, which I recommend, you will be able to get a massive bang for you buck. And getting a decent case from coolermaster will allow you to change out parts even faster.
If you do decide to build your own pc, I recommend going with AMD if you are on a budget. Here would be a good budget build.
CPU: FX 4100 = $109
Ton of computer cases for around = $25
MSI 760GM-P23 motherboard = $53
Rosewill RV350 350W ATX 1.3 Power Supply = $30
G.SKILL NS 4GB (2 x 2GB) 240-Pin DDR3 (memory) = $23
Western Digital AV-GP WD1600AVVS 160GB (hdd) = $77
Microsoft Windows 7 Home Premium SP1 64-bit = $100
MSI R6450-MD1GD3/LP Radeon HD 6450 1GB = $43
LG 22X Super-Multi DVD Burner = $16
Grand total = $476 You would be incredibly happy with a build like this for years to come. This build in a retail store would be $900+
Graphics card is even optional on this because the board has the ATI Radeon 3000. You could even get a build cheaper than this done buy using the AMD APU series chip and cut another $50 to $100 off this.
Check out newegg for some good budge laptops if you absolutely have to go that route. Something this
http://www.newegg.com/Product/Product.aspx?Item=N82E16834230240
or use this filter
http://www.newegg.com/Store/SubCategory.aspx?SubCategory=32&name=Laptops-Notebooks&Order=PRICE