Networking 3 simple questions

[Marvin Aguero <maguero@racsa.co.cr>]

Guys,

I guess these three questions are simple for those who are familiar with
Debian. I would really appreciate some help on these matters.

1) How can I know which IP Address I have been assigned if debian is
configured as DHCP? Something like ipconfig on the Windows world.

2) If I configured my machine as DHCP while installing it, how can I change
it to use an specific IP Address?

3) The opposite, if I have the machine configured with an specific IP
Address, how can I change it to use DHCP?

Thanks in advance for all your help.

-Marvin