I've had a look at the Dell site as I can't fault the Dell laptop I've got, so that's my personal choice - there are some other good makes out there. I'm surprised at how much prices have come down actually, they have more ram and bigger hard drives than my main PC 
To be honest, even the low end Dell 1525's look like they will be powerful enough for your mums friend - and its about half the budget:
Inspiron 1525
Intel® Core™ 2 Duo Processor T5800 (2.0 GHz, 800 MHz FSB, 2 MB L2 cache) 
Genuine Windows Vista® Home Premium SP1 - English 
15.4" Wide Screen WXGA (1280 x 800) Display with TrueLife™ 
Integrated Intel® Graphic Media Accelerator X3100 
2048MB 667MHz Dual Channel DDR2 SDRAM [2x1024] 
250GB (5400RPM) SATA Hard Drive 
DVD +/- RW Drive (read/write CD & DVD) 
1 Year Limited Warranty - Collect & Return  
£389 inc delivery + 1 year warranty.
These other ones also look good:
http://www.ebuyer.com/product/147754 - 17" Toshiba P300 £420
http://www.ebuyer.com/product/149335 - HP 6735s £390
http://www.ebuyer.com/product/152652 - Lenovo 3000 N500 £350
They all have slight diffences such as screen size, but all are powerful enough to run office/internet/music apps quickly (but games won't run well on any of them).