SELECT "PCI-Express" FROM table_39046 WHERE "Memory" = 'ddr2' AND "Model" = 'nforce 520'
What is the PCI-express with a ddr2 memory and a nforce 520 model?
CREATE TABLE table_39046 (
    "Model" text,
    "Processors Supported" text,
    "FSB/HT Frequency (MHz)" text,
    "Memory" text,
    "PCI-Express" text,
    "SATA" text,
    "PATA" text,
    "Sound" text
)