I will lay this out in step by step process.
1. Download the Megapack to your desktop.
2. Extract the files to your desktop.
3. Open My Computer.
4. Go to Hard Drive (c:)->Program Files->Glest->Techtrees
5. Open your megapack folder on your desktop.
6. There should be a folder called techtrees. If there is, open it. If not proceed to step 7.
7. There should be a folder called Megapack. Copy it (by right clicking on it and clicking copy).
8. Go back to your Hard Drive (c:)->Program Files->Glest->Techtrees folder. There should be a folder called magitech in it. If there is, right click and paste your megapack.
9. Open Glest.exe from the Glest directory, and try to use the Megapack Techtree instead of magitech.
10. If your game loads without error, please tell us.
11. If it doesn't work or you can't understand my instructions, PLEASE respond and tell us all you can. Glest (and the megapack) are too good to be passed up because of an error.
Also, look at the topic "Installation Problem (Megapack v4)". It might also help you, because it helped Durhal, another new poster.
P.S. Welcome Kallion0!