Ipswich is within close proximity to London, trains run every hour between London and Ipswich
Depending on where you are coming from in the UK, most routes will take you via London. From London you want to take the tube (Or a taxi) to London Liverpool Street.
Once at Liverpool Street Station, you can take the train from there to Ipswich.
For more information on route planning, see NationalRail.co.uk
Trains run daily between Amsterdam and London.
The average cost is ~£130
Once you have arrived in London, you will need to take the tube from St Pancreas to Liverpool Street Station, where you can get a train to Ipswich
The earlier you book, the cheaper it is, as with most things!
For more information see Eurostar.com