Does the old user account have the same name as before , or has it been changed to 'xyz (deleted)' ?.
If it has a usable name, just go to System Preferences - Accounts & create a new one with that exact name.
Click OK when "A folder in the Users folder already has the name 'account name'. Would you like to use that folder as the Home folder for this user account?" appears. Note: This will correct the ownership of all files in the Home folder, and avoid permissions issues with the contents
You can then logout & into the 'new' one.
If the name needs changing : follow https://web.archive.org/web/20130919225809/http://support.apple.com/kb/HT1428
rather than the current version at Apple
-------------------------------
If you want to continue using the new account you've already made, but access the old folders :
Select the old account home folder in Finder, then use Finder - File menu - Get info (command I). Open the 'Sharing & Permissions' section at the bottom, then click the padlock icon at bottom right & authenticate with an admin name & password.
Click the + button & add your new account name to the list, then select it & change 'Read only' to 'Read & Write'.
Now click the gear icon at the bottom & choose 'Apply to enclosed items...'