your Intel(R) PRO/Wireless 4965AGN supports IEEE* 802.11a, 802.11b,
802.11g and 802.11n standards, so you could go with a 802.11n router
instead of the 802.11g if you wanted and that will provide a longer range.
and as for the 2.4/ 5 GHz. frequency band
Copied from a goolge search ...................
Operating at the 5GHz radio bands has several advantages over the more common 2.4GHz band:
Better penetration
Better scatter
No abnormal adsorbtion by water or damp
Larger number of non-overlapping channels which means less radio congestion
OFDM over the whole speed range (better for non line of site operation)
On the downside, the Free Space Loss for 5GHz is about 6db worse than 2.4Ghz but, on the good side, the UK permitted power levels are 3-10db (depending upon the actual frequency) higher than 2.4GHz. This means, if you are using 5GHz for long range site-to-site connectivity you need to use a higher power level to cover the same distance.
However the raised permitted power levels and the better non-line-of-site capabilities makes it the preferred method for short range building-to-building connectivity and for in-building use.