I would look at the new HP g62...
http/www.shopping.hp.com/series/category/notebooks/G62t_series/3/computer_store?jumpid=reg_R1002_USEN
(sorry if the link doesnt work, I am new to the forums)
anyways, for $599 before tax, you will get:
new core i3-330 processor
free upgrade to 4gigs of DDR3 memory
free upgrade to 320g 7200rpm hard drive
regular integrated graphics ...etc etc from there
The nice thing about this laptop is the styling change, from the normal g60 series to this, they dropped the 10 key numerical pad, but the look of this is really spiffy.
IMO, one of the best things about HP is that you can set up a student login which will save you about 10%, this exact spec'd laptop would be $550.99. You end up with one of the newer processors on the market, ample speed ram, great speed HD and a good looking machine under budget.
Regarding the DM3 and that TX series that you are looking at, the Intel CULV processors are nice in the DM3, but only the higher end ones (SU7300 and SP9300). I would only build something with the SP9300 at the moment otherwise you are putting something together pretty slow (SU7300 speed is ~1.6ghz and the 4100 ~1.3ghz). That TX series for sale is only a single core and one of the earlier generations of touch laptop/tablets, I would not spend the money on it (though the add on accessories are nice) you would be wasting money on an older machine you would need to upgrade within a year or so.
Hope that helps.