
Go for it, bevb. You can demonstrate your computer skills in your letter of application :-)
Big ticks for: reliability, highly motivated, able to maintain client confidentiality, excellent telephone manner and communication skills (and that includes excellent listening skills), able to keep calm under pressure, able to maintain and update client records, able to self-manage workload and work as part of a team, quick learner, flexibility to accommodate changes in work patterns where needed. You might be handling cash, so perhaps you've done something like this before.
About your computer skills. Don't worry that you haven't got an ITQ, just think about the programmes you use daily/regularly: MS Word, Excel, Access, Outlook, etc. You may have advanced skills in some, intermediate in another or competent in the use of...and so on. Explain how you use different programmes--you might keep records for your own dogs (thinking about a certain recent exchange of admissions about the use of spreadsheets to track shows and performance of our dogs..:-O) .The fact that you are self-taught should just emphasise your capacity for learning, self-motivation, etc.
Draft your letter, and see if there's someone you know who has experience of appraising applications. Get them to read it to make sure it follows a logical order. You might start with any qualifications or experience, then think about your skills in the context of the requirements of the job and finally your personal attributes.
It's exactly like going in the ring--have confidence in your abilities! Passion goes a long way, but just show them you are really the whole package! Best of luck with your application :-) and let us know how you get on.