http://help.squarespace.com/guides/domain-mapping-with-dreamhost

 DNS Settings:

DOMAIN	CONFIGURATION
TWO LEVELS (E.G. MYWEBSITE.COM)	point A-record (IP address) to 198.185.159.144 198.185.159.145 198.49.23.144 198.49.23.145
THREE OR MORE LEVELS (E.G. WWW.MYWEBSITE.COM)	CNAME record to “ext-cust.squarespace.com“

 On the Dreamhost Side:

From the panel,  Go to your  Manage Domains Page and make sure the domain is DNS only. If you have hosting on the domain, use the “remove” button under the “web hosting” column:

Once the domain is dns only, click the dns link under your domain name and add these records:

Custom DNS Options:

Name: subdomain, leave blank for naked/root domain

Type:  type of dns record, such as A record, Cname, TXT

Value: Target

 

Settings Needed for this setup:

Name:  leave blank for naked/root domain

Type:  A

Value: IP records are listed above

---

Name: www

Type:   Cname

Value:  listed above

 

Note: This guide has been created to help simplify setting your domain up. The service you are pointing your domain to, DNS can/might has changed. Always check the hosts official page to verify the records.