Well, there are a whole lot of variables you want to address. Sam asked some important ones. If you are using LogMeIn, you will not have the RDP port open or the RDP service active, and your user will not necessarily be in the appropriate group. If you do not see you username on the Windows 7 box in the output of either command once you paste them into the Command Prompt, you will obviously not be able to RDP into your Windows 7 box.
net localgroup administrators
net localgroup "remote desktop users"
Another question: Are you connected to an Active Directory domain? When you open a RDP session, select Use Another Account. You will notice that under password is a line that says DOMAIN:. What is after that is important. Are you trying to connect with domain credentials? If so, that means the domain should be mentioned there. If not, you need to make sure you a specific about which credentials. So, if you are using local credentials (I mean local to the remote computer you want to RDP into, not the Win 2k8 server), you need to specify your want to authenticate against that. So for username, put in HOSTNAMEOFWIN7BOX\yourusername here. This should not be a problem but was for me at one time (I cannot remember if it was NT 6.* to NT 5.* boxes or vice versa).