Highly unlikely to benefit you at all, a dual core is perfectly fine, as is 2GB RAM although you can get away with less, particularly if you aren't building a very large installation. Focus on the video, networking and audio chipsets and search for their model numbers on the wiki and here to confirm compatibility. nVidia is the way to go for video - 6200 up is fine, you may want something in the 8XXX or 9XXX series if you hope to use hardware video decoding acceleration in the future (not currently supported, but coming), but don't go overboard on video as it isn't necessary. Intel NICs are popular (remember you will need 2 NICs for the core). Audio should be fine if the manufacturer has a Linux ALSA driver that is compatible with kernel 2.6.22-14.
For DVB-T, you might want to wait for support of the new HDHomeRun DVB-T that was just released in Australia. The older ATSC version is plug n play compatible with LMCE, and it shouldn't be long before the new version is added. Failing that the only one I can suggest is the only one I have used which is the Nova T 500, but be aware there are some annoying hardware bugs with that... may not affect you, may do... *shrug* But you will find plenty of other suggestions on the forums and wiki for DVB-T. If it works for them, it will work for you, irrespective of which country they are in, as long as it is DVB-T.