Yes.
The same as with wireless G card and G router.
Yes, you can. Wireless N devices are reversely compatible with G networks.
Yes.
You can use router of G or N type and the same type wireless adapter. Of course you can use wireless N adapter with G-type router and reverse.
802.11
In the wireless properties choose "compatibility mode for G" or something like that. If you do so your router will allow both types of wireless cards G and N.
Yes, it will. It will work with A, B, G, and N standards.
A Wireless G router provides Wireless access to 802.11g compatible devices
Yes it is backwards compatible
yes it can
A wireless router "N" has one of the fastest speeds available. It is more costly than the basic wireless router speed of "G". To ensure getting the fastest speed, be sure both the wireless router and wireless card have the same speed. Most laptops with built in wireless cards only have a speed of "G". The network runs at the slowest speed that is being used. An upgraded card may be needed.
If you have free PCI ports then any (but your router supports for instance only wireless G it's better to buy PCI card with wireless G support and not less).