I had pretty much the same problem, though I installed the full Delphi 2009 along with the existing Delphi 2007 and found that it broke my previous exe files. I uninstalled Delpi 2009 but had to fix it by editing the same file (though it was in a different directory on my machine: C:\Documents and Settings\All Users\Documents\RAD Studio\dbExpress\dbxdrivers.ini). However, there were more lines than just the one that is mentioned above. Luckily, I had a backup of the ini file from before the Delphi 2009 installation. Here are the two sections in case anybody needs help with this:
[Oracle] - FROM DELPHI 2007
DriverUnit=DBXDynalink
DriverPackageLoader=TDBXDynalinkDriverLoader,DBXDynalinkDriver100.bpl
DriverPackage=DBXCommonDriver110.bpl
DriverAssemblyLoader=Borland.Data.TDBXDynalinkDriverLoader,Borland.Data.DbxDynalinkDriver,Version=11.0.5000.0,Culture=neutral,PublicKeyToken=91d62ebb5b0d1b1b
DriverAssembly=Borland.Data.DbxCommonDriver,Version=11.0.5000.0,Culture=neutral,PublicKeyToken=a91a7c5705831a4f
GetDriverFunc=getSQLDriverORACLE
LibraryName=dbxora30.dll
VendorLib=oci.dll
DataBase=Database Name
User_Name=user
Password=password
BlobSize=-1
ErrorResourceFile=
LocaleCode=0000
Oracle TransIsolation=ReadCommited
RowsetSize=20
OS Authentication=False
Multiple Transaction=False
Trim Char=False
Decimal Separator=.
MetaDataPackageLoader=TDBXOracleMetaDataCommandFactory,DbxReadOnlyMetaData100.bpl
MetaDataAssemblyLoader=Borland.Data.TDBXOracleMetaDataCommandFactory,Borland.Data.DbxReadOnlyMetaData,Version=11.0.5000.0,Culture=neutral,PublicKeyToken=91d62ebb5b0d1b1b
[Oracle] - FROM DELPHI 2009
DriverUnit=DBXOracle
DriverPackageLoader=TDBXDynalinkDriverLoader,DBXCommonDriver120.bpl
DriverPackage=DBXCommonDriver110.bpl
DriverAssemblyLoader=Borland.Data.TDBXDynalinkDriverLoader,Borland.Data.DbxCommonDriver,Version=12.0.0.0,Culture=neutral,PublicKeyToken=91d62ebb5b0d1b1b
DriverAssembly=Borland.Data.DbxCommonDriver,Version=11.0.5000.0,Culture=neutral,PublicKeyToken=a91a7c5705831a4f
GetDriverFunc=getSQLDriverORACLE
LibraryName=dbxora.dll
VendorLib=oci.dll
DataBase=Database Name
User_Name=user
Password=password
BlobSize=-1
ErrorResourceFile=
LocaleCode=0000
Oracle TransIsolation=ReadCommited
RowsetSize=20
OS Authentication=False
Multiple Transaction=False
Trim Char=False
Decimal Separator=.
MetaDataPackageLoader=TDBXOracleMetaDataCommandFactory,DbxOracleDriver120.bpl
MetaDataAssemblyLoader=Borland.Data.TDBXOracleMetaDataCommandFactory,Borland.Data.DbxOracleDriver,Version=12.0.0.0,Culture=neutral,PublicKeyToken=91d62ebb5b0d1b1b