What happends If I exceed my RAM limit

Forget what I said, I clicked the wrong board. What he said.

So it looks like the specs are just 2GB max. However, some people seem to have gotten it working with 4GB by:
1) updating to the latest BIOS
2) using 2x2GB sticks -

Check out these posts:
1) http/vip.asus.com/forum/view.aspx?board_id=1&model=P5PL2-E&id=20091117203615765&page=1&SLanguage=en-us

2) http/www.tomshardware.co.uk/forum/269575-30-problem-p5pl2

As to whether those suggestions above actually work... you can't know unless you actually try. But there are two separate posts with people claiming to have got 4GB working. Might be worth a try if you don't mind shelling out for the 2x2GB DDR2 sticks.

It has to be in pairs for it to work in dual channel mode (doubles the performance by splitting writes across a pair of sticks). So it will always drop to single channel mode with an odd number.

However... you're likely hitting the MB limitation there. People on the forums I quoted above claimed to get 4GB working, but they tried 4x1GB with no luck, it had to be 2x2GB.
I suspect 3x1GB will have the same issue... it's a no-go. Worth updating your BIOS though and checking. Though I suspect it ain't gonna happen unless you have 2x2GB.

ASUS support lists it here: http/support.asus.com/download.aspx?SLanguage=en&m=P5PL2-E&os=17
I would expect there to be instructions included in the download. It shouldn't be too difficult.

I upgrade my Lenovo U510 Ram from 8GB to 16GB... crucial said max was 8gb... but then I looked up my cpu chip and it say it can handle 32GB max (i7 intel 3517 1.9-3.0 Mhz) Didn't see too much difference except when I multi task it seem smoother...also bought a SSD Hard drive and made it into an external HD which speeds up my comp while I'm doing Photoshop and Alias 3D work for school. Still Alias crashed once and I always get a msg when starting up the my graphic card is under spec... looking into overclocking my GPU but a little skidish. I rather drive to campus and use their computer than burn out my laptop...

System Diagnostics Log
Alias SysInfoCheck Version : 1.00.00
Date of Tune : Tue Sep 23 01:45:23 2014

Machine Configuration
Machine Name : RICK-LAPTOP
Operating System : Microsoft (build 9200)
Processor 1 : Intel(R) Core(TM) i7-3517U CPU @ 1.90GHz
Number of Logical Cores : 1

Memory Configuration
Total Physical Memory : 16258 MB
Available Physical Memory : 12326 MB

3D Device
Vendor : Intel

WARNING : Your current Graphics Hardware (video card) is below Autodesk
recommended levels. Alias might run, but may have bad display performance
or instability. Please see the link below for more details and a list
of hardware recommendations.

Video Processor 1 : Intel(R) HD Graphics Family
Video Processor 2 : GeForce GT 625M
Video Memory : 3136 MB
Video Driver File Version : 10.18.10.3621

OpenGL Support
OpenGL Version : 4.0.0 - Build 10.18.10.3621
OpenGL 2.0 - Supported
OpenGL Shader Objects - Supported
OpenGL Vertex Shader - Supported
OpenGL Fragment Shader - Supported
OpenGL Vertex Buffer Objects - Supported
OpenGL Frame Buffer Objects - Supported

Input/Pointing Devices
Device 1 : USB\VID_093A&PID_2510\6&14154DBE&0&2
Device 2 : ACPI\ETD060A\4&1CB455D3&0