I wouldn't spend that much on a secondhand lappy from Ebay, why not just buy a new lappy direct from Dell for not much more for a 15" unit.
see
http://www.computer-sale.com.au/lapt...n-notebook.php .
I don't think 10" netbooks (mini-lappys) are worth the price , they aren't much cheaper than a 15" notebook.
I've a 5 year old Dell Inspirion 5100 P4 3GHz 15" (ultrahigh resolution) screen that been a great unit and does everything I want to do .... including engineering stuff such running engineering modeling apps.
When one day I buy another lappy , it'll be another Dell , maybe dual or quad core 17" when the price on these falls a bit more (not any time soon as I'm happy with my existing lappy).