(Edit: I am assuming you're using Feisty. Should work on any Ubuntu releases though.)
As far as learning Ubuntu just keep doing what you are doing. Read as much as you can and use it constantly. Eventually you will get used to it and think Windows is the confusing one. If you want good piece of reading material try the Ubuntu Guide
. This is a great source of information. Plus since it's a wiki it is 100% up-to-date.
Now for the problem at hand. If you open the terminal (Applications>Accessories>Terminal) and type winecfg it will open a window that looks like window. If you haven't done this part yet, even I have forgotten a few times, you should go through and properly set-up wine. Then go to Applications tab and select the cashbook.exe then select it and change the windows version to Win98. Sometimes the *.dll emulation is better in 98 than 2000; the wine defualt. Try running the app again if it still doesn't work run
again and select cashbook.exe go to the libraries tab and select the ddeml.dll file and set the overide to native,builtin. (This is done by selecting the ddeml.dll and then hitting the edit button.) If there is still and error change the windows version back to 2000, but leave the ddeml.dll overide the same.
The linux world is full a trial and error. All because something works on one system doesn't mean it will work on another. In order to give you any more help you will need to run the app from terminal and post what you get on the thread. Open terminal and run
if there are spaces be sure to put a "\" or it won't work.(ex: c:/Program\ Files
To install the latest wine open terminal and run
wget -q http://wine.budgetdedicated.com/apt/387EE263.gpg -O- | sudo apt-key add -
sudo wget http://wine.budgetdedicated.com/apt/sources.list.d/feisty.list -O /etc/apt/sources.list.d/winehq.list
sudo apt-get update
sudo apt-get install wine
if you do this there shouldn't have any problem. If you do then it's not you there's something else at work. Hope this helps.