On both my laptop and desktop running Ubuntu 12.10 64bit the custom folder selection and adding for games under settings appear as in the attached image.

Desktop system info:

Processor Information:
    Vendor:  AuthenticAMD
    Speed: 3724 Mhz
    6 logical processors
    6 physical processors
    HyperThreading:  Unsupported
    FCMOV:  Supported
    SSE2:  Supported
    SSE3:  Supported
    SSSE3:  Supported
    SSE4a:  Supported
    SSE41:  Unsupported
    SSE42:  Unsupported
    
Network Information:
    Network Speed:  
    
Operating System Version:
    Ubuntu 12.10 (64 bit)
    Kernel Name:  Linux
    Kernel Version:  3.5.0-21-generic
    X Server vendor:  The X.Org Foundation
    X Server release:  11300000
    
Video Card:
    Driver:  X.Org Gallium 0.4 on AMD HEMLOCK

Driver Version:  2.1 Mesa 9.1-devel (git-8cf552b quantal-oibaf-ppa)
    Desktop Color Depth: 24 bits per pixel
    Monitor Refresh Rate: 60 Hz
    VendorID:  0x1002
    DeviceID:  0x689c
    Number of Monitors:  2
    Number of Logical Video Cards:  2
    Primary Display Resolution:  1920 x 1080
    Desktop Resolution: 3840 x 1080
    Primary Display Size: 20.08" x 11.30"  (23.03" diag)
                                            51.0cm x 28.7cm  (58.5cm diag)
    Primary VRAM Not Detected
    
Sound card:
    Audio device: VIA VT2020
    
Memory:
    RAM:  15921 Mb
    
Miscellaneous:
    UI Language:  English
    LANG:  en_US.UTF-8
    Microphone:  Not set
    Total Hard Disk Space Available:  120085 Mb
    Largest Free Hard Disk Block:  65201 Mb
    
Installed software:

Recent Failure Reports:

Laptop system info:

Processor Information:
Vendor: AuthenticAMD
Speed: 1800 Mhz
4 logical processors
4 physical processors
HyperThreading: Unsupported
FCMOV: Supported
SSE2: Supported
SSE3: Supported
SSSE3: Supported
SSE4a: Supported
SSE41: Unsupported
SSE42: Unsupported

Network Information:
Network Speed:

Operating System Version:
Ubuntu 12.10 (64 bit)
Kernel Name: Linux
Kernel Version: 3.5.0-21-generic
X Server vendor: The X.Org Foundation
X Server release: 11300000

Video Card:
Driver: X.Org Gallium 0.4 on AMD SUMO

Driver Version:  2.1 Mesa 9.0
Desktop Color Depth: 24 bits per pixel
Monitor Refresh Rate: 59 Hz
VendorID:  0x1002
DeviceID:  0x6741
Number of Monitors:  1
Number of Logical Video Cards:  2
Primary Display Resolution:  1920 x 1080
Desktop Resolution: 1920 x 1080
Primary Display Size: 13.58" x 7.64"  (15.55" diag)
                                        34.5cm x 19.4cm  (39.5cm diag)
Primary VRAM Not Detected

Sound card:
Audio device: ATI R6xx HDMI

Memory:
RAM: 7461 Mb

Miscellaneous:
UI Language: English
LANG: en_US.UTF-8
Microphone: Not set
Total Hard Disk Space Available: 593360 Mb
Largest Free Hard Disk Block: 89660 Mb

Installed software:

Recent Failure Reports: