The wireless network structure that you describe is called ad-hoc, which is the mode for wireless devices to directly communicate with each other. The alternative when using a router is called infrastructure mode.
For most manufacturers of wireless adapters, 802.11n is only possible in infrastructure mode, which requires a router. Without a router, you won't get beyond 802.11g. You should also get a router that allows setting an option for "N only", so as to force all laptops to this mode.
For example, this is what Netgear says:
IEEE wireless standards are used for
all NETGEAR wireless products.
Standards IEEE 802.11b and IEEE
802.11g specify that when in Ad-Hoc mode, wireless products only need to
support 11 Mbps. These IEEE standards
apply to "b", "g" and "Super G"
To get top performance, use Infrastructure mode instead.
And this is what D-Link says:
Q: Why can´t I get the advertised speed and performance when in Ad-Hoc
A: D-Link wireless products follow the IEEE 802.11 standards. The 802.11b
and 802.11g standards specify that
Ad-Hoc mode only needs to support up
to 11Mbps. For best results, use an
access point or wireless router and
set your adapters to Infrastructure