RAID or not RAID

I'm installaing a VMWare GSX Server on a RHL Ent.3 WS.

I will install two Windows 2003 with Exchange Server and two Windos 2003 domain controller.

I have some doubtes.

1.

I can't buy a NAS or SAN.

I will use a Proliant ML350/370 with 4Gb RAM or more and two Xeon 3Ghz.

Is better to use RAID (I think 10 type) or not use RAID level.

The raid level 10 is the best?

2.

Is better to use the growable disk or fixed disk?

How much is more fast the fixed disk?

Thanks

Luca P.