Oracle Database Express Edition (XE)

I'm new to Oracle and I'm taking an SQL college level course using a text book entitled "Guide to Oracle 10g". Our text book came with Oracle Developer Suite 10g (9.0.4.0.1) but no database. We adopted the 10g Express Edition (XE) as the database. I have both the database and the Developer Suite loaded on Windows XP Pro. I've been using the database for months now and it runs fine and the Developer Suite installed OK.

However, I would like to use some of the Developer Suite apps (for learning purposes) with the database but I can't seem to log on to the database through the Developer apps when I open them and use my 10g XE database user-name and password. For starters, I would like to see if I could use the edition of SQLPlus (release 9.0.1.4.0) that comes with the Developer Suite because it has configuration options that are not available in the SQLPlus command line version that 10g XE contains (which otherwise works fine).

When I open SQLPlus (Developer Suite Version) and try to log on with my database user name and password (and no host string), I get the error:

ORA-12560: TNS:protocol adapter error

I did search the discussion forum first and also reviewed some Oracle pdf's including the concepts pdf but came up empty. I would greatly appreciate any suggestions on how to succeed or a determination of the compatibility of 10g XE with the Developer Suite. Thanks kindly.