Install instructions:

1. Double click on 4350BPCEA.exe
2. Follow the on-screen prompts to extract the driver files
3. Launch Add Printer Wizard
4. When prompted for the Manufacturer and Model click on Have Disk
5. Browse to the following location C:/OKIDATA/B4350/English.
6. Click on OK
7. Follow the prompts to finish the driver installation

For Windows Vista, here is what OKI said on its B4350 driver:

The printer driver for this model is included on the Windows Vista DVD. Because it is resident in Vista, this model does not require any additional software or driver downloads for installation.

To install this model, simply plug the model into the system running Vista and it should be automatically detected and installed.

The resident Vista driver fully supports this models printing capabilities.

In fact, OKI has a wide range of printers that are natively supported by Windows Vista. Check out the list below for complete listing.

B4100; B4200; B4250; B4250-Black; B4300; B4300n; B4350; B4350-Black; B4350n; B4350n-Black; B4350nPS; C5300n; C5300nccs; C5400; C5400dn; C5400dtn; C5400n; C5400tn; C7100; C7100dxn; C7100n; C7200; C7200-MarketingEdition; C7200-RealEstate; C7200ccs; C7200n; C7200n-MarketingEdition; C7200n-RealEstate; C7300; C7300ccs; C7300dxn; C7300n; C7350hdn; C7350n; C7400DXn; C7400n; C7400nccs; C7550hdn; C7550n; C9200; C9200dxn; C9200dxn-ProStudioEdition; C9200dxn-StudioBuilderEdition; C9200n; C9200n-MarketingEdition; C9200n-StudioEdition; C9200nccs; C9300; C9300dxn; C9300dxnColorSignage; C9300n; C9300nccs; C9400dxn; C9400dxnccs; ML186; ML320; ML320Turbo; ML320Turbo-D; ML320Turbo-n; ML321; ML321Turbo; ML321Turbo-D; ML321Turbo-n; ML390; ML390Plus; ML390Turbo; ML390Turbo-n; ML391; ML391Plus; ML391Turbo; ML391Turbo-n; ML395; ML395C; ML420; ML420-Black; ML420-Serial-Black; ML420n; ML421; ML421-Black; ML421-Serial-Black; ML421n; ML490; ML490n; ML491; ML491n; ML520; ML520n; ML521; ML521n; ML590; ML590n; ML591; ML591n; ML8810; ML8810n; PM3410; PM4410

Alternatively, you can try the Free Driver Scanner.