I broke down your questions ans answered them below:
1) I wondered on shared hosting if you use Round cube for web mail.
Roundcube Webmail is no longer offered at DreamHost. The new and modern alternative DreamHost currently uses is Atmail. View the following article for further details: http://wiki.dreamhost.com/Atmail
2) Also how good is support for helping to install MySQL, scripts etc
While we do not assist with any Web Design or Development for our customers, we do Offer 24/7 Live Chat and Email support, along with callbacks as part of our premium support: http://wiki.dreamhost.com/Contacting_DreamHost
3) Can you pay the bill by Paypal?
If you are opening a new account, a credit card must be used to initially open it. This is to prevent fraudulent accounts from being opened. After the initial payment is received and the account is approved, you may make subsequent payments using any of the accepted payment methods listed here: http://wiki.dreamhost.com/Payment_methods
4) I am based in UK so can I still use you?
We are a US based web hosting company with data centers in Virginia (east coast) and California & Portland (west coast) - while we do not have a data center in Europe, we still have plenty of international customers including the UK!
If you have any more questions please be sure to hit up our Sales Team here: https://www.dreamhost.com/support/