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I am not sure what version of XOOPS you are using so I will tell you without the details. You set the blocks you want visible to visible and what page(s) you want them visible on. Then set permissions for those blocks for each group. So, if you want anonymous users to have access to the modules and blocks then you must grant them permission. Give them Module Access to each module you want them to be able to have access to, and put a check in any of the blocks you want them to be able to view too then click update group. You can find this in XOOPS 2.0.15 by going to administration/system/groups then Modify Anonymous.
HTHs
Quest
P.S. This works the opposite too. If you don't want them to see the Login Block you don't grant them permission to the Login Block by not putting a check in the Login Block for the anonymous user, etc.