I had already inquired to HTC about this particular issue and about adding addtional language keyboards...this is the response:
Thank you for your inquiry about the HTC Hero. I understand the importance of being able to use additional keyboards on the device. I will be more than happy to address this for you. Unfortunately, there is not a way to add additional keyboards to the devices. If you require symbols for certain letters, you may tap and hold the letter in question and select the accent from the pop up menu.
The user dictionary can only have entries added to it. You can do this while typing a new word, tapping on the "+" button.
I hope we have answered your questions in detail. Feel free to contact us again if you have any further technical inquiries. Thank you for contacting HTC Technical Support.