To get rid of old network settings, open System Preferences > Network. If the lock icon is closed, click it and enter the admin user password.... if you don't know the password, that's another question. Click the "Location" drop list an choose "New location". Give it a name (such as "Home") and click "Okay". Click the "Location" drop list and choose "Edit locations". Select the old location and click "Delete". Make changes to the new location if you don't need the simplest DHCP connection.
I have an iBook G4 that started with a French Canadian keyboard, got the language changed to Simplified Chinese and now I use it with one user English, one Chinese. I changed the several key caps that didn't match the English input (Chinese input uses the English key arrangement) after I got my hands on a German keyboard to cannibalise. Take a look to see if you have a French or English keyboard. The top row of letters will begin Q-W-E-R-T-Y for English and A-W-E-R-T-Y for French. If you have a French keyboard, you can remove the Q and A keycaps and reverse them. A few others are also arranged differently, but those two will drive you nuts both in typing and in key-combinations (⌘ Q to quit, ⌘ A to select all)
Typically, all possible languages are installed in OS X (around 17 if memory serves) for system menus, dialog windows, and error messages. You can easily switch it, next paragraph. There is a default language (in your case French) that would still poke its little head up when out of the user environment. Do this:
Open System Preferences (should be the fourth item under the Apple menu). Select the International pane (U.N. flag icon). Tabs left to right are Language / Formats / Input Menu. In Languages, drag the English to the top. Leave the Formats tab for later -- it's best understood for you after you log in to English. In the Input Menu tab, scroll down to British, U.S., or whatever you prefer. Put a check / tick. Uncheck the French or Canadian French or whatever if you don't plan on using French. If you do want to have the option to easily change the input method, put a check / tick for "Show input menu in menu bar". Quit System Preferences. Log out or restart. If you chose more than one input menu, you will see a flag icon in the top menu bar. Click it to change input to another "flag". If only one input is set up, no flag menu appears.
There is no trial version of OS X. If your iBook has a DVD player or combo drive, you can find a Tiger DVD for sale online for about US$150. Apple made a four CD set of Tiger that was sold for $19.95 to anyone who bought the DVD but did not have a computer with DVD player. Those are rare nowadays and cost as much as the DVD or more.
If you don't want to shell out for a system disc, get an external Firewire drive and use Disk Utility to "Restore" (clone) the hard drive to the external drive. Then if the system develops issues later, you can reverse-clone the system (lose new data but at least the system will run).
In the short run, after you get the language issue straight, you can create a new admin user account, log out, log in as the new user, and delete the old user. Use System Preferences > Accounts for this. The deleted user will be changed to a disk image and put in /Users/Deleted Users. You can then trash the disk image if you have no interest in it. Changing user accounts doesn't affect network settings.