As covered in this Apple Technote, Mac OS X 10.5 does not include support for the Classic environment.

Server for Intel: Macintosh OS X 10.4 and higher

Server for PowerPC (OS X): Macintosh OS X 10.4 and higher

Client for Intel Preview Release: Macintosh OS X 10.4 and higher

Client for PowerPC Preview Release: Macintosh OS X 10.4 and higher

Client Classic: Mac OS 9.1 through OS X 10.4.x (with Classic Mode)
Client runs in Classic Mode in OS X 10.1 through 10.4.x.

Engine for Intel Preview Release: Macintosh OS X 10.4 and higher

Engine for PowerPC Preview Release: Macintosh OS X 10.4 and higher

RADE Classic: Macintosh OS 9.1 through OS X 10.4.x.
RADE runs in Classic Mode in OS X 10.1 through 10.4.x.

Helix Utility and Update Collection: Macintosh OS X 10.3 and higher (OS X native) or Mac OS 9.1 or higher (Classic)

Server: Macintosh OS X 10.3 and higher

RADE, Client, and Engine: Macintosh OS 9.1 and higher.
RADE, Client, and Engine run in Classic Mode in OS X 10.1 through OS X 10.4.x.

Helix Utility and Update Collection: Macintosh OS X 10.3 and higher (OS X native) or Mac OS 9.1 or higher (Classic)

RADE and Engine: Macintosh OS 8.6 and higher.
Client: Macintosh OS 9.1 and higher.
RADE, Client, and Engine run in Classic Mode in OS X 10.1 through OS X 10.4.x.
Server: Macintosh OS 9.1-9.2.2. (Server is not OS X/Classic compatible)
Power PC 601 or higher
G3 or higher recommended for Helix Server
RADE: 12MB free RAM (minumum)*
Server:18MB free RAM (minumum)*

RADE, Client, and Engine: Macintosh OS 8.6 and higher. (Runs in Classic Mode in OS X 10.1 through OS X 10.4.x.)
Server: Macintosh OS 8.6-9.2.2. (Server is not OS X/Classic compatible)
Power PC 601 or higher
G3 or higher recommended for Helix Server
RADE: 12MB free RAM (minumum)*
Server:18MB free RAM (minumum)*

RADE, Client, and Engine: Macintosh OS 8.1 and higher. (Runs in Classic Mode in OS X 10.1 through OS X 10.4.x.)
Server: Macintosh OS 8.5-9.2.2. (Server is not OS X/Classic compatible)
Power PC 601 or higher
G3 or higher recommended for Helix Server
RADE: 12MB free RAM (minumum)*
Server:18MB free RAM (minumum)*

Macintosh OS 8.1 and higher. (Runs in Classic Mode in OS X 10.1 through OS X 10.4.x.)
RADE, Client, and Engine are not fully compatible with OS X Classic Mode. Server is not compatible with OS X Classic Mode.
Power PC 601 or higher
G3 or higher recommended for Helix Server
RADE: 12MB free RAM (minumum)*
Server:18MB free RAM (minumum)*

All products: Macintosh OS 7.5.5 through 9.2.2
Not fully compatible with OS 8.6 and higher
Power PC 601 or higher
(Helix Client supports MC68030 or higher)
RADE: 11MB free RAM (minumum)*
Server:17MB free RAM (minumum)*

*RAM requirements depend on the size and structure of the collection being opened and in the case of Helix Server, the number of Clients accessing the Server.

For questions regarding specific memory allocation for Classic applications, read "Have You Seen This Screen," posted October 21, 2002. If you still have questions, contact Technical Support.