I'm not that clued up on all-in-ones, but I can definately tell you that the Lenovo with it's Core 2 Duo has quite a bit more processing power than the HP's Athlon II X2.
On the other hand the HP's HD3200 graphics card is probably a bit more powerful than the Lenovo's X4500. Neither of them would be able to play games very well, but for multimedia/ office work they'd both be fine.
There is probably not much in them, they're both good makes. Only other noticable difference I can see is that the Lenovo has a standard 16:10 widescreen whereas the HP is the wider-still 16:9 format (which is apparently better for films). Hope that helps a bit!