Usage? Preferred screen size?

You will need more power for Autocad~
Can consider these:
13"
Asus U31Sd, i5-2410M + Nvidia GT520M@RM2999[1.78kg]; USB3.0 external OD, Asus optical mouse

Dell Vostro 3350, i5-2410M + AMD HD6470@RM2636[2.04kg], backlit keyboard, Belkin HDMI cable, 1 year accidental damage warranty

Sony Vaio VPCSB26FG, i5-2410M + AMD HD6470@RM3299[1.72kg], colors: White/Silver/Pink/Blue/Black
Sony Vaio VCSB28GG, i7-2620M + AMD HD6470@RM3999[1.72kg], colors: White/Silver/Pink/Blue/Black

Toshiba Portégé R830-1004/1005UB/1006UR, i5-2410M + Intel HD3000@RM3999[1.4kg], W7P, 2nd & 3rd year international warranty, Microsoft Office Home & Student 2010, Transformer flash drive; colors: metallic Black/Blue/Red

All these won't have a problem providing 4 hours of battery life with Wifi on and normal web surfing~

These are the basically the ones available for your budget
There's the Dell Vostro V131 and Acer 3830Tg as well, but they might have heat problems, so I din't recommend them

For battery life, i5-2410M; for better AutoCad performance, then i7-2620M~

Yeah, all can change to SSDs

I would recommend Toshiba Portege R830, its very light, comes with an optical drive as well as 3 years international warranty.
Followed by Sony Vaios, they have a dedicated GPU

Toshiba Portege R830 is only 1.4kg

The GPU in the Sony is nothing to shout about, but better than nothing la, especially if you're into some light gaming.. otherwise, don't have also good -> less heat

SSD upgrade will boost performance by a lot... battery life increase should be not much only iinm...

Toshiba or Mac depends on which platform you prefer, Windows or Mac OSX... and also software compatibilities and the "intensity" of your work

The Acer have Optimus so could have better battery life while the Asus don't have Optimus..
Multimedia: XPS 15
Games: DV6

If budget one, The OEM Intel X-25M 160GB from garage sales, RM4xx
Got more budget, can look at Crucial M4, Intel 510

Be aware that some of the Intel SSDs have the "detected as 8MB" problem, a firmware fix has been released, but I didn't catch up with the news

I don't quite understand what you mean?
If you want a clean copy of Windows installed, click on "Custom" at the menu where the button "Install Windows" is

Assuming you installed your Windows using that CD, then after you installed it you can delete the Windows CD image file

Type diskmgmt.msc on start menu, open it, there you can see one partition usually no name or named recovery.
Can consider also Dell Inspiron 13z or Vostro V131..

Right click the partition and delete volume..