The DELL is slightly faster (Processor) but has only 3GB of Ram (Acer has 4GB) Dell also lists the O.S. as Windows 7 Home Premium 64bit - the Acer doesn't say whether 32bit or 64bit. The Acer has a 500GB hard drive if storage is what you need (double that of the Dell) Both appear to have 3hrs battery life. The rest appears much the same.
John Lewis nearly always extend the Warranty to 2 years as they have done here.
I am a big fan of Acer (we have 3 in the family) and my son has recently bought this one for University - ACER 5732Z which is an excellent specification for less money (a saving for you students) click here
The only thing it lacks is a built-in Webcam but external webcams are cheap enough to buy (don't know why Acer didn't include one) This one has Windows Home Premium 64bit installed.
Something for you to think about.
Another good site to look at for Students if you are not already aware of it - click here
BIG savings to be had here.