greeting's

Constantine you might want consider going to www.insecure.org and snort.org or winsnort.org and searching for install information. Installing Nmap is as easy as unzipping all the files (dont forget to add registry information for "nmap_performance.reg" and in snort you have to edit a file (i am sorry i do not remember the name) but if you just go to download page of Nmap a complete instruction of installation and download procedure is given. As far as Nmap only command line version (Nmap 3.75) is available.

As far as your question about free (opensource) IDS snort is the best and Commercial IDS goes i still like snort but these are my opinion. It's better you search for both FREE and Commercial type of IDS on internet and decide which is best for you.

Breaking into a box which is firewall is possible but depends on many thing's. Like using a vunrabilty or using a vunrabilty in configuration by the user. All this also requires you too learn about how a firewall works ans how TCP/IP protocols work.

If you reall want to beome a elite cracker or hacker you migh want to consider not scanning using any portscanner becasue if they dont know you are going to crack and/or break into their server or if they dont expect you they want be looking for you (but this is just me). remember that portscanning is not the only way to findout which OS the target is running and also there are lot of ways you can fool portscanner (like Nmap) in OS fingerprinting.

As far as setting up and running Snort you might want to but Snort 2.1 by syngress (www.syngress.com)